If you can get to the area, the easiest way is probably to use one of the repair compression fittings.

You might have to actually make two cuts close together to remove a little bit of the line, but sometimes you can get by we’re just cutting right for the pinhole is and cleaning up both ends with some sandpaper or emery cloth if they will move enough apart to install the compression fitting and tighten it up.

Of course, having enough room to get to things is often the limiting factor.