Conveyor, Magnetic, Gravitational, Wind or Slippery Effect.....

I am trying to create an incline that challenges my character to climb. The incline is at about 30 degrees, from left to right. The character moves from left to right in 2D space using a simple flappy bird type mechanic. I need something to force my character to fall back pushing from right to left at slight varying speeds. I don't want it to be impossible to climb just challenging, to make the player work for it.

I have used 3 different conveyor scripts, and none of the other scripts seems to work on inclines (noted in their descriptions). Is there anything else I can try, I really don't want to scrap my idea.