Hi Hillbilly,
Am lookin at doing the same thing as the fridge here has a two keg limit. We just use a pluto gun via the open fridge door and when the pour rate gets low, just top the gas up and disconnect it.
Wasn't gunna worry about all these calculations and stuff. This way we gas the kegs when filled, to full pressure, turn off the gas, disconnect gas, and then place keg into the fridge. the gas line is then put onto a keg which is being drank and the pressure in the line is then dumped into that keg till no more gas is heard being transfered.
Was looking at doin a couple of double batches soon to boost stocks and just doing a regular gas top up of the room temp kegs (at a low pressure) till they are ready to go into the fridge. should be ample enough to carb the beer a bit as well as keeping a layer of CO2 on top.
This may sound a bit rough but so far have had no worries about beer in the gas line and the beer is well carbed.
Recon that if you give it gas for the first few days and then check if there is still pressure via the relief valve, things should be OK.