Exim is case-sensitive for usernames? Help!

Is there any way to stop Exim from being case-sensitive when it comes to usernames? I have several users on this server that were setup (before I got here) in the form of "JDoe." Before switching to Exim as the MTA, mail could be sent to either jdoe@domain.com or JDoe@domain.com and it got delivered properly. Now, however, mail to jdoe@domain.com is being rejected. This sucks, to say the least. Any fix? (I know I could add lowercase aliases for all the users, but that's not a solution -- just a time-consuming workaround.)