It's already there in a somewhat friendly format. The vector that is drawn for the directions seems to be an encoded string of actual coordinates. They simply decode it, scale it and draw it with some javascript foo.

I haven't had time to really play with gpsapp in a while, but the attached file was able to parse the google maps data. I got directions, clicked on the 'link to this page' and saved the page as plain html.

Then I fed it into the parser and it spit out something that looks like it would be a valid input file for gpsapp. It doesn't strip down the turn-by-turn descriptions yet, so gpsapp will probably repeat itself like 'turn left at turn left at that street' and quite a bit of code was simply cut and pasted from parse_mapsonus.

edit: updated the script to add the destination address as the last waypoint.