If the ramp he has is good otherwise, sounds like you just need a cover.
You want the cover to have at least 1/2" holes though so the UVB can pass through.
One option is to cut a piece of eggcrate to size, and friction fit it in.
Another option, which I recently implemented myself, is an old fridge rack. If you have a spare fridge or oven rack, just put that on top of the tank. The slats are big enough so the UVB can pass through, but the rack should be heavy enough so your turt can't push it up.
Here's what mine looks like on my 90 gal:
