Got it.
When a user connects to one of these systems there is an initial call to the 'UserLevel' database to get the various access levels that the user has for that system. All I need to do is have the front-end then call a stored proc at that point, that writes these setting to tables within the target database - pretty much using the code and table structures that it has now.
You may not think you have helped out there but you have - writing the problem down and then saying why suggested solutions won't work helps me to work on the problem.

I don't normally get as far as actually posting the issue - usually writing it out brings a solution to light. The Rubber Duck.