I figured this out today while making a game for the Click competition.

What you do is make your character and the conveyer belt. The events should be as follows:

(I will call the player character and the belt belt)

collision between character and belt
----set character's position to X )-1 Y)0 relative to character

now run your game. When your character starts running over the belt he will start to run slower. and if you stop while on the belt he will slide to the right.

If you want to slide to the left change the X to 1. if you want to slide up change the x to zero and the y to -1 and if you want to slide down change the x to 0 and y to 1 you could put a combonation to make it slide diagonally. Make the #'s bigger to slide faster.

I hope this is of use to someone.