I do it all the time. Go buy your commercial keg from the brewery or the store. Refrigerate it over night.
I use a counter-pressure filler setup. Put 10 lbs on your CO2 and hookup the Sankey tap. I do a hot water wash on the bottles then I soak them briefly in a 5-gallon bucket of water and 1 oz of Star-San, which I leave in the sink. Let them drain on a sanitized bottle tree, then place the bottles in the refrigerator or the freezer. I spread out a towel in the freezer so the bottles avoid contact with other frozen food things there. You need COLD bottles to avoid foaming. I do the actual bottling on the kitchen counter. Also, hoist your keg up on the counter, then elevate it another 10-12". I set mine on a sturdy bucket to get the height. Also, go get a cake pan to place under your bottles. I set mine on a towel on the counter. It will all get wet. Turn off your fluorescent lights and shade the windows. You don't want UV to skunk beer while it is in the clear PVC plastic lines. I prefer clear lines so I can see what is going on with the beer. There is an art to it, my first couple times it was a mess, but once you get it down, no problem. I use Grolsh-type swing top bottles. Make sure to sanitize everything including your lines. I used -4 and -6 AN fittings on my lines for easy disassembly and cleaning. I also built a couple hose fittings with -4 and -6 ends to hook up to my garden hose to really blast out the lines after use.
1. Pull bottle from freezer. Place it on your bottling pan and insert filler into bottle.
2. Press down on the rubber stopper. Incidentally, I use a wire tie at the top of the stopper to prevent blow-by.
3. Turn the 2-way valve to the C02 position, and then purge bottle of Oxygen with C02 using counter pressure filler.
4. Sometimes you can unseat the stopper briefly to let the gas out faster, but make sure to return the stopper into the seated position and make sure the bottle is pressurized.
5. Swing the 2-way valve over to beer fill position.
6. Slowly crack open the stainless vent valve and beer will begin to flow.
7. Continue filling. You will start to get foam out of the vent valve.
8. Let the foam keep coming until you get beer coming out. Turn the 2-way valve into shut-off position.
9. Be patient. If you fill too fast you can get foam. Sometimes you need to open the valve up a little more as the beer approaches the top of the bottle. You will spill out about a bottle or two of beer (as foam) in the course of bottling a 5.25 gallon keg. If you are a real animal and like flat beer, you can pour this off for drinking as you are working.
10. Use a little LED flashlight, it helps to view the beer level in the bottle.
11. Take a clean paper towel or cotton cloth and lightly wrap it around the rubber stopper when you remove it from the bottle. This avoids spraying beer out on the counter and your shirt.
12. Wait a couple seconds and the foam should come up. You should always cap on foam to avoid Oxygen in the bottle.
13. Some bottles don't foam up all the way. For those you can dribble a bit more beer out of the filler valve, just shift it slowly in the beer direction and place the tip over the top of the bottle. This will complete the filling and bring the foam up so you can cap.
14. Finally rinse off the bottles under tap water and towel dry.
15. I label all mine with a strip of colored PVC electrical tape. White for light beer, Yellow for lagers, Orange for Ales, Green for IPA's Black for stouts (maybe brown if you can find it.)
16. Takes about 2-1/2 hours from setup, to bottling to cleanup for a typical 5.25 gallon Keg.
I refrigerate the finished bottles, they should be good for months that way. I don't store them at ambient because some of the beers are not "live" (some have been filtered, so no available yeast) so they should be refrigerated to keep fresh and to prevent early degeneration. If the beer you are buying still has a live or semi-dormant yeast culture in it, you could probably be safe storing it at room temperature for a while, but you could easily over-carbonate the bottles (which are already starting with adequate C02 pressure). Probably best to keep it under refrigeration to make sure all is OK.