Somehow (it took some effort), I managed to get a small amount of beer into one of my gas lines - maybe a couple of drops. My options seem to be 1) RDWHAHB, 2) try to purge the line with some sanitizer, or 3) replace the line.
It seems to me that, in a chilled CO2 environment, it would be difficult for bad bugs to infest the line, so maybe option 1 is fine. But then again, a few feet of line is pretty cheap, so go with 3. No votes for 2, so far.