What is a good hack for a sushi rolling mat?

Hands or plastic wrap.

My Japanese friends just use cling wrap or quite often just their hands.

If you are having trouble rolling the seaweed, then cut it into smaller squares, lay out the rice and fillings on the table, and teach the eaters how to make temaki sushi cones. It's like a build your own sushi adventure, kids love it.

My local sushi place uses plastic wrap.

p.s. Don't Japanese sushi masters ever make sushi rolls using just their hands? Obviously, the seaweed outside, not inside-out.

These are guesses. A Silpat baking sheet. A bamboo placemat. A dishtowel sprayed with a neutral oil to avoid sticking.