It can be done and isn't all that hard. There are a bunch of different fittings on commercial kegs, but most all of them use the same fitting for gas in/beer out. You can remove the bung on many (all?) of them, but some are easier than others. Some are really politely threaded...we used to use them at a brewery I worked at, but I don't see them on commercial kegs too much.
The more typical type are removed by pulling out this spring loaded little band that fits around the bung and holds it in. So, you just need to buy/steal some kegs and the appropriate fitting, attach a agas line in and a beer line aout and proceed as normal.
But I'm not sure you've thought out all the difficulties. Cost is the least among them IMHO. For starters, how would you chill 4 or 5 15 gallon kegs? Even a chest freezer wouldn't cut it. If you have access to a commercial walk-in freezer, then you're cool, but otherwise, this is kind of a deal killer. You wouldn't be able to condition the beer if you can't chill it.
And what about cleaning them? You can't get your arm in there to scrub, so most commercial breweries use harsh chemicals, usually very basic, to clean them. That's pretty scary stuff to mess with since it melts skin. I'd avoid if you can.
Why not just fill 10-15 cornies, then build yourself a cool looking tap/dispensation system. I have my taps mounted on a cool redwood board on my back deck, and you have no idea what the beer is stored in. What, after all, is so much cooler about the big kegs? They're much much worse if you're thinking about using a hand pump like you'd have at a tailgate party because your beer will go flat and get skunked by the introduction of oxygen.
You're much better off to dispense with CO2, and build yourself a nice tap setup or jockey box with 2 or 3 taps. Then you have some classy stuff that folks love at parties (believe me), and no one knows or cares whether your beer is in big or little kegs. It comes out of taps like at the pub, which is way cooler anyway.
Have fun and good luck!