UHMW is available as a tape too...
A magic material from my old bag of engineering tricks. The surface you apply it to will have to be smooth, clean. Might need to sand and paint it first.
But that is a tough problem. If you can get more slope (doubt it) and drop at the end do that too.
Other happy-hour brainstorms: can you vibrate or shake the ramp somehow with a wire or rope?
Does stop/start during retrieve help or make it worse?