Tried that before-- the problem is, once a collision has occurred, the smooth "falling" flow is broken. When the grenade "jumps down", the Y vector gets reset.
I've attempted one solution where I track the Y vector number prior to the collision with the jump-thru floor, and then set the Y vector to that number immediately after the collision. Unfortunately, the "falling" flow still gets ever-so-slightly broken using this method.
(M.A.D. are my initials. I'm not the least bit angry, really!)@madguy90