Hmm, yeah, good point, I suppose in commercial setups they don't have to worry about yeast at all. Personally I wouldn't worry about actually eliminating headspace, as the beer would be falling into a pure c02 environment so you don't have to worry about oxidation, and if you ever needed to actually reduce pressure in the keg for some reason (filling bottles from the tap, for example) you wouldn't be able to do so as opening the pressure relief valve would just result in beer going everywhere. I prefer for my beer to go in my mouth But that's just me!
Also, just out of curiosity, why not just keep one keg outside the fridge or keep the one in the back not hooked up, and pull it forward when the first one kicks?
Good luck to ya!