Easiest option:
RDWHAHB, you're overcomplicating things. I've been in your shoes before, and posted here for advice, and that was the general consensus.
http://www.homebrewtalk.com/f35/transporting-recently-filled-keg-345618/
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
and,
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.