I don't have a seal separator for you (I have one but I still need it), but I just discovered you don't need the vise blocks. Just wrap a shop towel around the top of the stanchion tube where your vise will clamp down, and gently tighten the vise. As long as you don't overtighten such that you deform or crack the stanchion, you can get it tight enough without any damage to use a seal puller. I did this successfully a few times, without any issue.
If you are set on the vise blocks idea, just get a block of wood, drill out the stanchion tube hole, then cut the block in half and use those as the vise blocks. That's what I was going to do if my technique above didn't work (but it did!).