Editing Garmin data?

I went for a run tonight and stupidly forgot to stop my gadget at the end of it. Is there any way to edit the data to remove the extra 5 hours it has recorded so I can store it on Fetch with the correct time/distance? 

Oddly, despite being sat motionless on my coffee table for the extra five hours it was left recording, it has somehow added five miles on to the distance I covered...

There's a couple, depending on how technically minded you are. From the garmin training centre software you can export an activity to an xml file which is a text description of the activity, that you could edit and then save.

Alternatively, plenty of the online tracking services allow you to do this in a more user friendly way. Runkeeper for exapmple lets you edit the points and time on a map. After which you can then export the amended activity.