On PC, you can join empty servers that are all 1-player start and join games and just capture flags in vehicles then swap teams and recap - or you could do this with a friend and not have to swap teams as they will cap the flags you cap allowing you to cap them again.
On 360 and playstation 3 I think you can only do the 2player one as I am not aware of any 1playerstart maps - I know there aren't on Ps3 but I don't own an xbox to know XD