TMG 2010 w/ Exchange 2007/Exchange 2010

All:

We are looking for a way to utilize ActiveSync and OWA proxying rather than redirection between Exchange 2010 and Exchange 2007 servers.  The reason behind this is that we don't want to have users have to manually change their phones after their mailboxes have been migrated to the Exchange 2010 server.  Without TMG, leaving the External URL blank would allow both ActiveSync and OWA to proxy rather than redirect.  Can this be achieved with TMG publishing the sites?

Thanks in advance!

-Micah-