Ok, I just ran a test with some new code that creates an .NETbased sidebar gadget and I was able to get the dll unloaded from the sidebar process so it can uninstall successfully! This is good news for all the people that can't seem to get around this issue (and there's a few of you). I'll get going on a solution and post the results here. If you want to be emailed when its ready, just ping me and I'll add you to a list.
Want a hint as to how I solved it? Take a look at this post's tags 🙂