Just came across this program on the App Store.

It's allows you to do basic edit GSP tracks on Google Maps and Earth imagery. It seems to be aimed at cleaning up tracks you've recorded rather than route planning.

https://itunes.apple.com/us/app/adze...7341'mt=12

The lite version won't allow you to move points on the track, so seems limited to basic clean up tasks.

Use Adze to edit GPS data like a champ

Looks like another useful addition to the Mac Users GPS Toolkit.

cheers
Paul