Adding a Halyard with mast up

[Brian Duff]

If there are exits near enough you may be able to use a piece of 1 by 19 cable , 3/8" or 1/2" try different sizes, to knock some holes in the foam from below and drop a much heavier weight through that hole, or try a snake from the top and jam it through , either way get some sort of passage through the blockage, and tie something bigger to the messenger, and pull that through your mast to grab and jam the foam to one end or the other of the spar where you may pick/tear it out and then drop a proper messenger on weights to get a fair lead, and your done.
Might find the rig has to be pulled to get the obstrution out.