I'm really late to the party on this (found it in a search for PEM nuts), but I've done this with a drill, bolt, ratchet and a little PVC.
You need some STRONG hardware, but essentially you drill a hole where you want the bolt for the toroid to go. I typically use 1/4-20 stuff for this. Get a grade 8 or better 1/4-20 bolt that's plenty long (longer than you'd need for the toroid for sure) some matching nuts, some thick flat and fender washers (you might need to upsize a couple of times) and a high pressure PVC or metal pipe.
The order would go something like this:
Bolt --> (thick) Flat washer (or two) ---> hole in bottom of chassis ---> 1" (or so) I.D. metal pipe/PVC --> large fender washer (multiples for extra thickness/strength) maybe a flat washer, and finally a nut.
Grab a wrench and a ratchet and go to town. The 1/4-20 bolt will pull against the chassis panel and the 1" I.D. pipe will limit the area the 1/4-20 bolt will deform. Keep crankin' on the ratchet until you create a deep enough dimple to mount the toroid.