This idea is exactly correct
" My first thought was to just create a temporary media pool and move the tapes to that media pool"
If media is in a media pool not being used for any backup, the media will never be touched. You can also protect the sessions on the media to Permanent, this will prevent the media from being used
I suspect that teh media pool these tapes are in are using Free Pool. Right-click on the media pool go to Properties, then to the Allocation tab. If 'Use Free Pool' is checked, un-check it, click Apply. You shoud then be able to move the media to whatever pool you want, Once you are done, re-enable 'Use Free Pool'