Security policy differences between Outlook AddIn 2003 and 2007

Question

I have written a managed AddIn for Outlook 2007, and am now tasked with porting it to 2003. The addin downloads DLLs into the local user profile folder, then reflectively loads them for execution. This all works just fine in Outlook 2003, even with Click-once deployment.

The issue Im experiencing is that the AppDomain does not have Execution permission on the dynamically loaded DLLs in Outlook 2003. I do not know the folder location of the dynamically loaded DLLs at installations, so I cannot use an installer CA (such as http://weblogs.asp.net/mnissen/articles/427490.aspx) to grant full-trust to these DLLs during installation.

Can anyone explain how AddIn activation differs between Office 2003, and Office 2007, and how I might solve this problem?

Thanks!