not a problem. You can give him up to 25% or so without a problem. and yeah, if your friends gets sand (the dead stuff) give him a few cups of your ls, and have him spread the ls over his sand. Same with lr, if he just gets base rock you can give him a piece of lr or he can buy some base and some lr. Depending on the size of your tank you could give him more water. I have 75, so I could easily give enough to fill his tank (room for water displacement and such).
the live stuff will seed the dead stuff.
he'll still have to cycle though...
if he's using cc and not ls, put ls in the foot of a panty hose and place on top of cc.