You might look at

http://technet.oracle.com/doc/server.815/a68003/01_11ext.htm

You have to modify the tnsnames.ora and listener.ora files and start a Listener process exclusively for external routines.

I've not done this before and am only going on what the documentation says. I will be very interested in knowing if you're able to make this work.

HTH,

Gregg