Hi Rowland
I presume you meant to attach something?
What if we use an in body filter like this one to create an air tight chamber in front of the sensor similar to ccd's.
http://www.sciencecenter.net/hutech/filters/ffilter.htm
But if heating the glass face is the only option we could use smd resistors on the glass face to heat as they would provide higher resistance than nichrome wire for the space that's available.
Or if we replace the aa filter with clear glass and create an air tight space in front