GroupWise 8 Outlook 2013 on the same PC (headaches)

So I have a problem that's been making me pull my hair out and was hoping someone could offer some advice.

OS - Windows 7 Professional x64 (all Windows Updates installed)
GroupWise version - 8

I have a user (who is a local admin on that machine) who is unable to properly run GroupWise. He simply gets the "GroupWise is not properly installed" error when he tries to open the client. I have found that I can go to the Control Panel, select the "Mail (32-bit)" option, and remove every information service entry from that list, and then I can open GroupWise again. One time. Once I close GW, it gives that same "GroupWise is not properly installed" message.

I've seen this in the past where GW and Outlook don't like to be on the same machine (most of the problems in those cases being related to the address book and GW insisting that I create an Outlook profile). My fix has always been to simply "custom" install MS Office and exclude Outlook, since we don't actually use Outlook. For the most part, that has always worked like a champ. However, to the best of my knowledge, Office 2013 is an "all or nothing" thing that doesn't allow you to do a custom install, so I end up with a machine that's going to have both installed.

Am I doing something wrong? I typically install Office first, then the GroupWise client, make sure GroupWise is set for all its defaults, and I'm good to go. But this is the first time I've dealt with Outlook 2013 and GW on the same machine. Is there a more proper way to make GroupWise 8 behave when it's on the same machine as Outlook 2013? I've just got this particular user running with WebAccess until I can get it figured out. Since we're going to be doing a lot more Office 2013 installations in the near future, I'd like to get this figured out and not have to deal with it again.