I'm not sure there are (m)any silver bullets. The three basic approaches are 1) separate DBs, 2) separate tables and 3) shared db/tables: http://msdn.microsoft.com/en-us/library/aa479086.aspx
I don't know if there are an "silver bullets" for this so you might just have to brute-force code it. If the app is fairly simple, just check who's logged in and show the appropriate data. You might also research if Web2py's "group" functionality would help. Sorry, this isn't too helpful.
