Case sensitive domain selection

So, while it might be possible to have drop down lists to choose the appropriate domain and subsequent AAA servers to authenticate users I decided to be lazy and just put a domain field into the logon page in VPE. I then created an Empty action with a different branch rule for each domain. Based on that they hit the correct AD Auth server and all seems to work nicely (if not efficiently). My problem is that the branch rule on the empty action that I use looks like:

expr { [mcget {session.logon.last.domain}] contains "contoso"} (== works as well).

 

This works fine except for obvious case mismatch issues. Is there a way to convert the domain to lowercase so this will always match? Or a better way? Thanks.