If you pre-process the bracketed exposures before stitching as Klaus suggests then the tool should work to reduce co-ordinate records to one per shooting position in your XML - although I don't know if it works with XML files created by the Panoneed head:http://www.anderson-mark.com/paxw/
Could you not also just do a 'dummy' shoot with bracketing set to 5 to create the XML file you want?
The Panoneed records two .xml files, one has one bracket for tonemapping before stitching, the other has all brackets for stitching before tonemapping. Very convenient! In this case, I had two sets of brackets that are not all that useful to the shot (too over or under exposed), and I was looking to save some time exporting them out of Lightroom. Since it's a several gigapixel spherical image, it's 540 photos or so and a lot of storage space/time for unused files. However, setting up the Panoneed to fake shoot it again would take about an hour, and it took about that long for Lightroom to export them anyway and then manually deselect and delete them out of PTGui. I had to add them to begin with for the .xml file to make any sense to it. Now that I've done all that, I wasn't overly pleased with the results and I'll probably tonemap before stitching, haha! At any rate, such a tool to decrease or increase a bracket in an .xml file would be incredibly useful for odd situations.