Lion Mail and Portable Home Directories

I'm administering a network of about 45 machines that we've recently updated to Lion from Snow Leopard. We're still using Snow Leopard on the server. On client machines, we're running into sporadic issues where users (particularly those that move from computer to computer) are unable to open Mail.app and get an error that they aren't able to import their messages. This is the kind of situation described here and here.

I've tested the solution at the latter of those discussions, and it does indeed prevent the import failure allowing users to get in to Mail.app without too much trouble, however I'm running into a pretty serious drawback with it. Users still have to go through the import process each time they log into a new computer (or if their mobile account is deleted, e.g. if their normal computer is re-imaged, etc).

Is there anyway to prevent users from having to repeatedly import like this, or am I stuck with that lesser evil of frequent, but at least successful imports?