So you can pass in the imagecache presets namespace directly into your GMap view for use in pop-ups.
I had (apparently) figured this out a while ago but had Dan going through the code print_r'ing views variables to try to figure out where we could intercept the file ID and change the path to imagecache... and the path was already imagecache.
Any imagecache type you create can be chosen for CCK image
Moral of the story, when you're dealing with Views, assume it can be done through the user interface. There is full and amazing Imagecache support of Views.