Could you use zip-ties on it? If it can anchor between knobs, you just want to really crank on it. If it's even a little bit loose any side-to-side movement could push the knobs sideways, which is bad.
I did this with an Eventide Timefactor and it worked perfectly. I didn't have to take of the giant rubber foot on the pedal. It would've been hard, if not impossible, and I didn't want to damage the pedal.
I used two zip-ties to anchor it to a Pedal Train board, and it worked perfectly. The ties never even touched the knobs; that's how tight I had them on there. When I removed everything all of the knobs moved smoothly. They weren't stressed by lateral movement on the zip-ties, and the housing was as strong as any pedal, so it worked just fine for me.
If you have a different pedal board, I don't know for sure what to tell you. I would still try zip-ties before you mangle the back of your pedal. All I can advise is what I have tried and had success with. I don't know of any velcro strong enough to stick onto rubber pedal feet. It's worth a shot. Zip-ties are dirt cheap at Home Depot; big bag of them for maybe five bucks.
Either way, best of luck. Just don't do anything that you even think could cause damage. No knives, super glue, or anything like that. The idea the put on a new plate of metal is a good solution, IF you can successfully cut out the right sized plate and drill holes etc. That is really a good solution as well.
But I would go with the cheapest option first: zip-ties. Why not? You can just cut them off if they don't work for you and then you're back where you started, with no harm done.