RDWHAHB, you're overcomplicating things. I've been in your shoes before, and posted here for advice, and that was the general consensus.
I had a 2 hour drive. What I ended up doing was just filling the keg as normal, then leaving it for a little while I cleaned up, etc. By the time it was ready to go in the car, there was already a bit of pressure in the headspace from the CO2 coming out of solution. I pulled the pin and released the gas. After loading it into the car and jostling it a little bit, I got another good hiss from the pin. Periodically during the drive I'd pull the pin, the gas would just keep coming out.
So in conclusion:
1) RDWHAHB, the amount of oxidation isn't really a big deal unless you want to age the keg for a long long time.
2) If you vent the keg periodically, chances are most of the air will be pushed out by CO2
3) If you're really really worried about it, I would just naturally carb the keg. That way the yeast would eat up the O2.
Buying extra equipment seems a bit silly IMO.