Hi,
You could use the same "Hot Tap" procedures you would use on any process line. You basically weld a connection to the pipe, and then use a machine to bore through a valve into the pipe. You did no mention the line sizes, but if they are small, you could forego the hot tap machine, and just use a drill to install the hole in the connection, and a ball valve to quickly close off the connection after you drill it. If your connection is small, and if you are quick, you shouldn't lose too much air. However if you choose not to use a hot tap machine, and something goes wrong during drilling your plant is down until you can fix the problem (i.e. a broken bit halfway though, etc.).
Good Luck George Griggs
Sr Process Controls Engineer