Well, you'd need some sort of loop to go through and send the messages one by one I think.
Be careful though... if you've got alot of users, you're gonna really slam your w3t_Messages table.
That's really been the limitation of making it a feature. A site with 30,000 users sends a mass PM and slams their Messages Table with 30,000 rows simultaneously.
Your database could get very big, very quick.
