OK, I've set up the following Challenge;
http://www.endomondo.com/challenge/sK8HKV2HVEU
It runs from now till the end of October and is based on who does the fastest 10miles in that time. Obviously no-one's going to be checking, but try and keep it to mainly off-road rides :-)
I've set it up as a private challenge so you may need to click something to say you want to join it.