Since none of you know the info on where the balls go, here:
There is a cavity, in your pelvic region, that is hallow. The testes sit here until they descend from birth, and they also slowly rise up into the pockets when they get extremely cold (They need to stay a normal temperature or the sperm will die).
You can push them up there yourself. If you need to apply pressure, you are doing it wrong. Just lift a leg, and pull your dick backwards behind you, and 'split' the two balls on either side. From there, you can easily just slide it into the area, and presto! It is virtually painless, and if you just use a piece of tape (medical please, do not use duct tape on scrotum unless you shave) to keep the scrotum skin tight so they can't slip back down, then just take a tthicker piece of tape and tape your dick between your ass (if you want to, you can just have underwear hold it there).
It will mess up your sperm count slightly if you keep them up there too long, but if you aren't aiming to impregnate a girl in the next few days, then it is 100% harmless.
Hell, if you want to get serious, you can take clear medical tape and get them pulled tight, and get everything snug and settled in, and you can pull off a bikini bottom that looks flat.
Krazy/Super glue is an alternative, but it is entirely useless unless you plan to do a photo shoot or something. Also, what i found best (I am a crossdresser/transgender), is if you take a piece of toilet paper and just wrap it loosely around the tip of your penis, and the shaft, before taping. it is thin enough to be unnoticeable through clothing, and it will prevent the pain caused by tape sticking.