Well, it'd be a pretty nasty hack, but you could always add a second submit button. If you name them both so that with javascript you can tell them apart, you could just ignore the first one. Now, to make it look better to the user, you could make the first one an image button where the image you use is something the user can't see. So, you'd have something like:
<input type=image name=submit_one src="my_blank_image.gif">
<input type=submit name=submit_two>
Then in your javascript, don't submit the form unless the submit_two button is clicked.
As I said, a pretty nasty hack but it should work.