My thoughts...
I had to take my raytheon sending unit down this winter for rehab, so I had the yard drop my mast. If you are thinking of attempting this while the mast is up you will probably encounter some type of sealant at the mast step where the wires penetrate the cabin top, in my case it appeared to be 4200. My suggestion would be to validate, through Hunter, that they indeed caulk this area. If so, the mast will probably have to be dropped, unless you can figure out a way to raise the mast off the deck and simultaneously get to the top to mount the sending unit and lower the wire down the internal conduit. The thing is that even if you where able to get a cable through the sealant, you don't want to have water penetrating through the deck. Sorry, but I think your only option is to drop the mast. Then you could pull up a small line attached to the masthead light wires which would then allow you to pull it allong with your new wind sensor wires back down. From there my wires are routed up through the port setee, behind the fuse panel, though the head cabinet, along the aft berth headliner, through the bulkhead, behind and above the disel tank( drill a small hole from in the aft berth next to hump), pull the wire through and then up through your pedestal guard. If it sounds like a lot of fun and frustration, IT WAS! But I will admit that after reconfiguring my entire Raytheon ST50 package(i.e.,wind, knot, tridata, autopilot) it was all well worth it. Seatalk is a beautiful thing. Good luck.