Yeah, my biggest question was whether the Lat/Lon data could be added "in place", without rewriting other data, and w/o re-encoding the jpeg.
On cursory glance, it seems that the GPS headers are additional, meaning that space is not already allocated in a standard EXIF header. It still might only be a matter of appending the data on at the end, but it doesn't look like it's going to be *that* easy. We have some code now that reads the EXIF headers, but nothing that deals with the additonal GPS stuff.