this is what I would do and I have been there many times.
First, cut two small holes below that extruding pipe. Run a coat hanger in one hole on one side of the pipe and then fish the end around the pipe and into the hole on the other side. when done, twistee the hanger in tight to hold it in place. Now you can do your operation without the pipe pulling away.
secondly, on this situation, its a good idea to install the radiator rubber hose connector that has screw clamps on each side to sinch up on the pipe, this way you can get in this area if you need to at a later date.