I have never done tried it, but I don't think it would work out that great... the trekking pole would allow you to cast, but it would hardly have any shock absorption and I think you would run a good chance of breaking the line or the fish shaking loose.
I have seen videos of people fashioning a pretty nifty fishing rod out of a stick and some eye-bolts for guides, I think that might take a few minutes to build, but might work better than a treking pole. There was a pretty good video of someone making one... I can't find it now, but the instructions similar to this: http://gsleaders.org/files/makefish.htm
Post whatever you come up with though, it's an interesting idea.