To my knowledge it cannot be done using out of the box rules. The only way I can think that you will be able to do this is to have some vba code in outlook. try posting on outlookcode (google it) you may have better luck there. I would be interested in finding out a solution though so If you do find out how could you let me know thanks.

Remember if the mailbox owner has the option "Send meeting requests and respsonses only to my delegates not to me" ticked in delegates. It would be a bad idea to move these mails to another folder as the outlook sniffer would not pick the meeting request up and it would not appear in the owners mailbox as tentative.