That's the reason it's NOT a timesink! You can just set a skill to train and do RL stuff while it's chuggin away. You can put in as much time as you want really, apart from the time to get the money for skillbooks (but that's not much time anyway).
Any half-decent driving sim will let you set the clutch to a pedal. :)
Btw: check out www.racesimcentral.com if you really want to get into this stuff.