How can I change the default port (9000) that Play uses when executing the "debug run" command?

I usually run a Play 2.0 app play "~run 8991"

to run my app on port 8991 instead of the standard port 9000 as described in this other question.

But how can I change the default port when I want to debug my application? play "debug run 8991"

* still uses port 9000; 8991

will be ignored.

(Note for closing voters, this is not a hoax of the linked question. It says nothing about debugging.)