I use M5 threaded inserts in a supplemental wasteboard on top of a double wasteboard. I inserted flanged threaded inserts from the bottom of the board. It is mounted to the big wasteboard with countersunk nylon 1/4-20 bolts. The 1/4-20 inserts in the big board aren’t going anywhere. And the M5 in the supplemental board aren’t going anywhere.
I recorded the extents that I was comfortable cutting on the XL (jogged as close to the rails as I could and wrote down machine position). I also took my .25" endmill diameter into account. I used one of the holes on the big wasteboard as a good approximation for my zero.
Just make sure that if you’re a day or so from replacing your Z you wait and do the measurements with the new Z. i did not.