[Zope] undo machinery mysteries

Is there a way to protect objects from removal due to ZODB compaction and still maintain undo and revision history? You could consider the the opposite of a 'Temporary Folder'. For certain documents, I would like to keep ALL previous versions in the object store forever- superpersistant, if you will. The best way that I can think to approach this is to keep my superpersistant objects in a second ZODB and mount it in a folder in my primary ZODB. I could then compact my primary without losing old revisions of my files. Is there a better way to approach this?