You would need to write a hook (see the pre-revprop-change.tmpl) to store the changes somewhere since revison properties are UNVERSIONED.
My thought would be to write the property to a temporary file (this would be based on the transaction number)and allow the update, then on the post-revprop-change pre-append this to the property and commit, this would require a dedicated user (this would need to be checked in the pre-revprop-change) that then didn't create a temporary file.
I've been thinking about this myself but haven't written it yet!
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