I had used the following method to help a couple of people to sort out a severely stuck mast. Here is how...
(1). You need a strong and firm anchor point. Your car's tow-ball will be ideal.
(2). A strong piece of rope. Rope about the thickness of your harness line would be ideal.
(3). You need to create a means to securely attach your mast. The attached diagram shows what an "abseiling rope knot" is.
(4). You need to tie up the loose ends of the rope as shown so that you have a closed loop.
(5). You need to have a long enough rope so that you have at least 30 cm of free-play. This is to build up the momentum when you give it a mighty tug.
Here are the details explanations...
The "abseiling rope knot" provide a dead grip on the mast. The tighter the rope is, the firmer the grip will be. The rope should be over the bottom section of the mast because it is fatter. Now you place the knotted end over the tow-ball,
with the bottom end facing away from you, and you are pulling on the tip end of it. As I said earlier, you should have at least 30 cm of free-play.
Now get at least two people to hang on to the mast. You then move the mast forward as far as the 30 cm of loose-play allows. You both synchronized 1-2-PULL. In fact, it is more like a strong jerking motion. You will, if you are lucky, see the base begins to move a bit. The rope will not give by virtue of its design. You can pour some water or may be WD-40 at the joint.
Of course, you need to make sure that the rope is a good, strong one.