Rebuilding Stoptech ST60 calipers - anyone done this?

I’m considering moving up to 380mm rotors.
Stoptech will sell me the necessary bracket to make my 355mm ST60 kit work with 380mm rotors. However, the piston sizes will need to change to keep the brake bias where it should be.

So the question is, does anyone know if it’s possible to buy a different piston size (with the necessary piston boot) to “convert” a 355 ST60 into a 380 ST60? Stoptech will not respond to my email on this topic. I figure from a manufacturing standpoint, all ST60 calipers are the same. The piston bores are actually all standard, and they simply replace the pistons within the bores with the appropriate piston and boot sizes to make 1 caliper work for a multitude of applications.

pic for visuals. Below is a shot of 2 ST60 calipers. Notice the piston bores look to be the same, but the piston sizes between the two kits differ. The smaller pistons actually sit in a pretty big piston bore, and the boot simply takes up the rest of the space.

http://image.superstreetonline.com/f/22252790+w+h+q80+re0+cr1/modp_0908_07_o%2Bproject_nissan_350z_stoptech_brakes%2Btrophy_vs_trophy_sport_stoptech_caliper.jpg