I suppose you have more answers to that question than I do. I have never tried to get Excel to work (at any capacity) on a machine that did not have an install of Office on it already. So you know something I do not.
This is the most complete tutorial I can find to create an MSI. There is mention of the regedit and bundling files etc. Not sure if you can adjust the order of the install. For instance, placing a sub key in an area before the parent key exists may be an issue. May have to run separate install using third party packager.
http://www.addictivetips.com/microso...lution-wizard/
You can also write VBA to edit the registry keys. I would not know if you need to add the registry keys to get the functionality you require or not. Including one of the compatibility packs for Office offered by Microsoft may be a benefit to you. Overall, what you are describing sounds like a hack and may not be stable going forward.