This is a bit expensive in that you have to create a separate connection for each database. Ok, it's not horrible, but we've found a better way - DB Links. This allows you to create a link from one database to another from *within* your table. Thus, you can make *one* connection, and then connect to the other databases via the links.
I think the drawback is that it doesn't test the listener, just the connection, but I could be wrong. Hey, I'm just learning about this, ok?
Oh, and Tora doesn't have support for DB Links yet - bummer. There is an RFE, though (#592157 on the sourceforge page if you'd like to chime in). At least TOAD supports it, though.