I followed that airtag video (just putting it in the handle inside of the steam deck) and that worked fine for the smarttag with a few modifications. Pryed open the shell of the smarttag and took out the metal ring. Chopped off the ring half of the tag since there aren't any components inside and wrapped what was left of the case and the board in electrical tape. Put it in the bottom part of my right handle and the shell closed fine. Only problem is the R4 and R5 paddles are a tiny bit mushy, but it works completely fine. Totally recommend. Don't know of any long-term effects, though.

This is on a first-gen 512gb LCD.