So I wondered if there was a better way to hold thin material and not worry about the clamps
Well what do you know tile leveling wedges will fit in the t-tracks with a slight modification with a pair of scissors
Best thing is they are super cheap and won’t hurt your router bits
Or you could use these.
as you can see useful on both thick and thin materials and very low profile as well and being strong as hell. use my clamps in making my clamps go to hilljackfab.com and see them in action too.
I have used Painter’s tape with superglue. The tape releases easily from mdf and the superglue is thin so removal isn’t difficult depending on what material you are holding.
If I mill really thin, soft stuff I superglue to a piece aluminium and then release with acetone.
I have never found the painter’s tape able to stick to the MDF spoil board because the surface is fluffy after surfacing. Do you seal the MDF after surfacing?
I seal my spoiler board with Seal Coat after surfacing. I use double-sided tape and don’t have issues with the tape not sticking. If anything, I have issues trying to pry large pieces off when I get lazy and use long, continuous pieces of tape. 
I made a jig for carving into round coaster blanks, and found the tape stopped sticking after a few uses. I resurfaced the round pockets, sealed with Seal Coat, and have not had issues after several uses.
Yes, with Shellac. It makes a significant difference.
I seal with danish oil. Hardens a treat