...every winter since I bought it.

Once the engine is completely warmed up, the warmth in the engine
compartment often allows it to let go (not much help if you need to open the
hood to jump the battery to get it started in the first place).

I tried thawing it out in my garage until the cable started working, then I
tried blowing air and lock de-icer down inside the cable tube - a little
difficult with the position of the cable. It helped for a while, but it
started sticking again soon after.

Whatever you do, don't force the handle under the dash, it will only break
and then you'll really be stuck. Sometimes it will free up enough to open
the hood, but will get stuck in that position (the catch spring is not
strong enough to overcome the sticky cable). You'll know that happened when
you close the hood and it will not latch itself. You can ease the catch back
into position (carefully) with a screwdriver.

Good luck.