Thank you all for the helpful suggestions.
Using email domains has worked just fine when the exclusion is permanent, but this situation is different, unfortunately.
With filters, it doesn't seem to work exactly as one would expect. Patrick, the way you describe it is exactly how I thought it worked. However, the problem seems to be that contacts are only pulled into the filter at the time it's created. So when I add that filter to the master exclude, then a new contact enters the system, the master exclude doesn't catch it. The filter itself might catch it, but if that's the case, it seems the master exclude works independently and doesn't refresh itself with the new records. Hopefully that makes sense.
With the program "add to shared list" solution, it's still slightly difficult because once a person no longer meets the criteria they have to be removed from the shared list as well. Adding the shared list as a feeder is actually a good suggestion, then additional steps can be used to see if they should still belong. Thanks Dustin.