Frenchy,
There's so much variation on how high testicles hang that I don't think forcing them to hang lower will cause any signifigant damage to your fertility. That is, as long as you don't injure yourself.
Red,
I use 2" harness rings from Lowe's and a sock for ball stretching.
You cut the sock so it's just a tube that's open on both ends. Place the sock over your scrotum/testes with the extra at the top. Pull your testicles through as many of the rings as you are comfortable with. Then pull the extra sock(at the top) over the rings and tuck it between the rings and your balls at the bottom. This is known as the "sock tuck trick" over at �other forum� in the huge low hanging balls thread.
I've done this for as many as 20 hours in a day(including sleep). It does take some getting used to, and loose pants. I haven't done this in about a month, but probably will soon. Mine are still hanging a lot lower than they used to, but I'm going to try for more "hang" later.
It definitely helps reduce the "turkey neck" effect, and maybe the "extra skin" you're talking about.