Never used DB2, but just thought I'd toss an idea out: could you possibly call your procedure such that the results go into a temporary table? Then you could follow up with a SELECT to retrieve them from there. Not the most efficient way I'm sure, but might at least work.

You might also search IBM's developer forums. They've got a pretty good collection of articles and I wouldn't be surprised if they didn't have an article on DBI and DB2 there.