Some Socket 7 boards have a PCI and ISA slot that share the same backplate slot, like my Asus TXP4:
I read here that both can be used at the same time, and wanting to add a PowerVR card I gave it a go. The PowerVR is ideal as it doesn't have any backplate connectors. Other good candidates would be a SATA or SCSI controller with only internal connectors.
The clearance between the cards is very tight indeed so I made up an insulating sheet to prevent any nasty accidents.
Zip ties come to the rescue once again.
The final fit, as you can see it's very tight. The PCI slot grips the card well but I added a 3M Command strip (easily removed double-sided sticky pad) to attach the PowerVR to the next card.