Just pull the sound out in the editing process..this can be done with most editing tools..better to ad your favourite soundtrack anyway.
I thought the software tool on their site used to do it, at least a year ago?
In any event use the VirtualDub freeware, also fast tool to snip bad stuff.
Use the "Direct Copy" mode only for that.
Cheers.
Try cutting an old headphone plug (that connects to camera) and put it in the ext mic hole).
Or is that new gp's only with ext.mic port?