Assuming for a moment that you could drill and tap the pipe, and that you could find "some kind of adaptor", you would have a very suspect connection that might fail. Moreover, the time and effort to do this would hardly offset the relatively simply cutting and threading a couple of pipe ends and buying standard plumbing fittings. I don't know how successful you would be with drilling and tapping, but it certainly would be a Mickey Mouse setup and Murphey's Law would dictate that when it failed, it would be either in the middle of the night on a weekend or while you were gone on vacation. You can rent or borrow a pipe cutter and a couple of pipe wrenches. Cut the pipe and remove the resulting two sections and take them to a shop and have them threaded. Shorten one of the pipes to allow the insertion of the tee, nipple, and union. Then reassemble everything using pipe dope or tape on the threads. There are times and situtations you can be creative, but this isn't one of them.