Dynamic Distro - Filter Help

In our environment we have different groups of users, and they have different formats of their EmployeeID. Some are all numbers, and some are prefaced with an alpha character. I am trying to come up with a query to only include users with an EmployeeID with no alpha characters. Is that possible? I know I can script this in PS and manage it that way (which I have done in the past), but to compensate for the learning curve of all the users using this tool, I would like to keep everything in the GUI.

Alternatively, is there a way to add a regular LDAP query to the membership rules? I don't see a way in the GIU to add each criteria and nest them so I can have AND and OR statements.