No obvious thoughts. I can modify the TC system to produce a GPX/TXC file from a given start point but that would take a bit of time if you need this soon.
Alternatively you can just edit the GPX file using a text editor. Just move all of the GPX "<trkpt> ... </trkpt>" lines before the lat/long you want to after the end of the last <"trkpt> ... </trkpt>" line in the file.
thanks. I will have a go!