Peter, thanks for the suggestions but I think I might just wait for VSTO
2005, the existing frameworks are just to flakey and the plumbing required
too complex. I can't seem to manage getting anything to work in repeating
elements and since I can't seem to attach to the plumbing to debug it I'll
have to give up for now.

There seems to be too many fragmented bits in this arena at the moment
(VSTO, IBF, Smart Documents) none of which quite do what you want them too.
It's almost as if you guys were using this as an extended public beta before
releasing a unified solution that actually does something truly useful.

Here's hoping VSTO 2005 actually works.