One of my favorite things to do! To me, bras are the pinnacle of being feminine, and are always an unremovable "must". I live in a small area, so going out en femme is just something I've never dared to do. However, bras can be relatively well-hidden, and I've ventured out in them from time-to-time.
Around the house, simple self-bondage works well. For instance, get donned in your outfit (bra included!), take the key to your cuffs and place them somewhere... a hard to reach place, somewhere outdoors, etc., and snap the cuffs on yourself. With a back-close bra, cuff hands in front, front close hands in back (hands in back are great if you put the key in a hard to reach place!). I usually put on a back-close bra, cuff my hands in front, and leave the key out in my mailbox. I live in a residential development with cluster boxes, and my box is about 1/4 mile away. Thus, with no shirt, I definitely have to wait until not just dark--but very late (when there's a minimal chance of anyone driving in). I can't put on a shirt or coat to cover the bra due to the cuffs. Anyway, I *could* take it off with scissors, so it's not 100% fool-proof.
Another way is to put on a cheap bra (it'll basically be discolored), and use a bottle of spray self-tanner (the darker the better!) and spray, spray, spray! Be sure to exfoliate the area very, very well beforehand eliminating as many of the dead skin cells as possible... this will make it doggonned near impossible to "scrub away" the tan. Once it sets up, you'll have a "bra" that won't come off for days. And if you have light skin to begin with and you use a dark self tanner, it WILL show through a thin shirt. You can also do the reverse if you have a helper... use Mehndi to draw a bra on your body, and you'll have a nice, dark bra that will last for weeks. Never tried that one... but tempting!
Lastly, if you REALLY want to get a bra stuck on you, then here you go. Again... this will ruin the bra. Put on your bra of choice, and begin gluing it on using superglue. Again--be sure to exfoliate the area to remove dead skin cells. Basically, once the bra is on I pull a small portion away from the body on the front left, apply a small line of glue to the front left, then the front right, and let the bra sit back on my body. I then do the same in the back and use a plastic knife to reach and spread the glue. I keep doing small areas in opposite portions until I have almost the entire band glued, and finish by apply glue to the clasps in the back. Benefit--it makes you VERY flexible! LOL! Now--depending on whether-or-not you want breasts, you can insert some breast forms before gluing the top seams of the bra. I usually don't do the straps unless I want them to be more visible, and if so, I'll pull them towards my neck a bit and place a dab of glue where it goes over my shoulders. Now... if the area wasn't cleaned (degreased) and exfoliate to remove the dead skin cells, it'll peel off--with a bit of difficulty--about anytime you want it off. But... if you clean the area well beforehand, you're going to be wearing it for a bit. It will eventually come off from body oils surfacing and as skin layers begin to shed, but be SURE you want to do it! If you want t live out the fantasy of being trapped in a tight-fitting bra for a day or longer, this will certainly do the trick. Also--it makes the bra a bit inflexible, and since it's adhered to your skin, it pulls every time you breathe. You will KNOW you have it on every second of every hour of every day. I actually did this this past Saturday when the wife was out of town for a few days, and it was exilerating! I applied the glue middle-afternoon, and by that night a couple of areas (right and left side under the bra) worked loose fairly easily. I was a bit disappointed, but everywhere else was firmly adhered. On Sunday I was getting a bit tired of it, especially after taking a shower and having to wear the bra wet for a couple of hours. I had worked a good portion of the bra free by that evening, but I couldn't comfortably work the back very consistently and finally got it off (feeling like my skin was ripping!) on Monday. Two days is more than enough for me, but if you want to expand it, just use some rubbing alcohol on areas where it works loose and reapply the glue.
Disclaimer--as for safety, superglue is supposedly non-toxic to the skin and to the body. After all, it was primarily created as a suture for cuts. BUT... I'm not a chemist or a doctor, and although I've seen where people say it's safe, just use your own judgement. I still have redness on my back where the last straps came off (today is Friday--4 days after), but I honestly think it's due to skin irritation and likely pulling a bit of skin off. Hard to believe, but I was ready to just get the bra off.
Anyway, when I started supergluing bras, I just dabbed a little glue here and a little glue there. It also leaves the bra a lot more flexible that way, and is easier to remove if you change your mind.
Other than that, I'm stumped. Sewing something rigid into your bra would be hard, and you need to be sure you can breathe! The chest has to expand
Let us know whatever you do!