It would probably be cheaper, and I know it would be a lot easier to just buy a set of rings from Walmart for a few dollars and take the part out that you need.
My personal opinion is that It would be MUCH, MUCH, better to just throw the see-thur mounts in the trash where they belong and take this opprotunity to replace them with a real set of mounts.
Nothing wrong with Weaver mounts. They work as well as anything, just don't look as nice as others, but the guy who thought up see-thru mounts should be forced to use them for the rest of his life as punishment.