I would ALWAYS put the code you want the ribbon to execute in the same template. However, the concept I would try is to point your ribbon at a macro in the same template that does:
1. Check that the addin is loaded and if not, attempts to load it
2. If the addin is still not loaded, tell the user that it wasn't found or loaded
3. Calls the macro you wanted in that addin

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Andrew Lockton
Chrysalis Design, Melbourne Australia