It's not advertised, but I added this feature in the past week, for up to 5 recipients.

Separate usernames on the "Username" line with a semicolon, like:

docjohn; candybear; kimmydawn

Up to 5 names. It will send the PM out to all 5 people at the same time.

I also added PM forwarding as a feature, so you can now forward a PM to another person if you care to.