Linepick alternative.. some idea?

Hi all,

I've experienced that Linepick is the slowest
function in the world.. I've observed how the game
framerate slowdown more than 25% and I would like
to change this command for another function.

I mainly use this function to position the foots of the enemies over the floor. I have aproximately 15 enemies in
the level, and the linepick function is:

Linepick(enex,eney,enez,0,-5,0)

Please, someone could point me in the right direction? What's the best way to implement a similar function?

Thanks a lot!