There are two things I use alot with my knives which should work good with spurs bits etc.
1- I put 3m packing tape on the opposite side of where I am engraving , then hot glue the piece to a block of wood. The word is oversize to the metal which alows me not to mar any metal surfaces. You can use any wood and cut it to different shapes. Plus you can put a hole lot more preasure on the wood with your engraving vise. When your done engraving pour rubbing alcohol between tape and metal and the bit spur will pop right off.
2- I get a product from
www.grstools.com called thermal lock. This is some kind of plastic which when heated in the microwave it turns soft (don't leave it in too long get to soft) then you take it out, put it on your spur then into the opened vise. Now you wait for it to cool. It cools very hard and will hold your object fine. One other thing about thermal lock is it bonds very well to plastic, but doesn't stck to metal. DON'T get it on your counter top, it don't come off. We broke the plaslic handle that is on the water tank we use to haul water and made a new one with just the center part of the plastic.
This will probably work the best for a set of spurs. I use an old micro wave thats in my shop. You can put the whole thing back into the micro wave, just put it on a plate and make sure it the metal can't touch the sides or it might arc. The other way is to make a two piece jig by incurting a thin piece of metal inbetween so you will have to parts.
Hope this helps
Rick