We use Nutsert brand at work. You can "rig" an install tool. You need a high quality "best" is likely allen drive cap screw, a spacer which you can make out of a nut and some washers. Oil threads, hold the spacer with a wrench and drive it in. You need to watch material thickness vs nutsert length.
I'm not to certain, tho, of long-term grounding integrity. "They could rust" between the insert and firewall.
Frankly, the "old school" method of grounding using the mounting, whether a VR, ignition box, or lamp sockets, was damn poor design
