You could use cardboard on the headliner to protect it and use a 12" block of wood to Push up on it and get enough gap to do it. You only need about 1" or so clearance to get a good weld around it. Piece of cake! Now that is if you are going to keep the headliner and not replace it. I will start the weld on top of the tube and wrap around the whole tube back up to the top on the other side......no stopping and starting the weld at all!
In my case it is coming out because there are a few little holes in it. It will get replaced when the new interior goes in it.:-D