I’ve found this thread probably too late for my reply to be helpful to harknell, but I ended up here because I had a similar issue, and a solution that worked for my situation.
Something to keep in mind with the sidebar is that the code of your plugin is available to you, just not through filters like the_content and others. If widgetizing is unappealing for any reason, you can make direct php calls to functions in your plugin.
This means putting a line of php code in the template, which harkin wants to avoid, but if you can set up your plugin so it can be a really simple line of code, perhaps that won’t be too much to ask of your non-techie users.
