Need help weight painting interior vertices (been stuck for awhile)

hey guys, I've been stuck in an animation project or a long time. where I'm stuck is weight painting so could somebody tell me how to paint the interior verticies? I have a model that has poofy sleeves and I cant get the inside of her sleeves, a friend showed me how awhile back but I can't remember how and he lives in puerto rico so he still can't respond to me, it was something like hitting Ctrl=+something I don't remember what though