did you ever find a solution to this?
I have a similar issue
Reposting here, as response via the mailing list does not seem to have been posted to the forum.
I wound up doing programmatic datasources. In my case, had one
Datasource going to a configuration database that had the configurations
(username, passwords, etc.) for the other DBs stored in it.
This was for JBoss 3.x & 4.x. Don't know how well this will work for
5.x, although there was some 5.x stuff in the late 4.x, so it might.
I didn't really solved the problem, I eventually moved to one data base.