APM 11.3 client side registry check - Case sensitivity issue

I've been looking on and off for a while now. We're trying to do the usual client side registry check in HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters\Domain to make sure the user is logging in from a PC that's joined to a domain in our AD forest. The problem is that we have 40+ domains in the forest and the registry checker is case sensitive and doesn't support wildcards or regular expressions (that I know of). So right now my APM check has 40+ OR statements in it, one for each of the possible domains in our forest. So my question is: Does anyone know how to make the check case insensitive or even better, get the value from a registry key into an iRule so I can use TCL to do a wildcard match at the forest level?