Its an Addin, so how exactly is
app.config, and make sure that it's
copied to dll directory?
going to help?
Basically you would need to create a file called Outlook.exe.config and put it in the Office12 folder with Outlook.exe (c:\Program Files\Microsoft Office\Office12)
If you do this it will get loaded, the only potential issue is that it is also available to any other addins that are loaded into the outlook.exe process.
A better idea is just as the OP suggested an use an arbitary config file copied to the targetdir and read it from there.