A long time ago, when I had a MB 220D, I picked up this device
from an accessory store. It was a cannister with two fittings
on it to take a windshield washer hose on one end from the
w/w pump, and then on the other end was a fitting for the hose
to travel up to the nozzle.

The rest of the device was this 5/8" pipe which you put in line
with one of your heater hoses (cut the hose, and put this in).
Surrounding the 5/8 pipe was a larger plastic pipe - sealed
at both ends, and containing the fittings for the w/w hose.

The way this thing would work is that the w/w fluid contained
in the plastic pipe would be heated by the water from the 
car's cooling syste{.

	
It worked quite well, kept the w/w fluid warm enough as not
to shatter the windshield. Unfortunately I couldn't find
another one...

Ric