There is an easy way to do this without having to have someone else race you. Find a race to join, i recommend a shorter race, then when the race is about to start do NOT touch your controller for about 5-10 seconds. you will see a message pop up on the bottom of the screen saying disconnected from server. once that pops up all the other players disappear out of your game. now go finish the race and you get credit for the win. Do it 9 more times and the achievement is yours. I expect it to be patched in the future though.