Using an airbrush to apply VEIL has already been explored, in-depth, on RD.net, for both G2 as well as G4.
As
Veil Guy cited, there's apparently no need to "thin" either solution - both can be applied "straight." Be sure to pay attention to the can's "shake-and-rest" instructions, though, as well as pay-heed to these fellow VEIL user's warnings and tips:
VEIL test on hayabusa - Radar Detector Jammer Forum -
sbfuller is a newcomer to RD.net, but this thread is, I think, honestly the best "how to" that I've ever seen. Although detailed pix can be seen on page 1 (including the before-G4, wet-sanded, picture), the most valuable post is
sbfuller's follow-up on page 2 (post number 15), in which he actually shows how he airbrushes the light housing.
Worlds longest VEIL post. - Radar Detector Jammer Forum -
erickonphoenix is a long-time user of VEIL, both G2 and G4. His application here shows how much darker and more "matte" G4 can get, with repeated coatings.
Airbrushing Veil - Radar Detector Jammer Forum Airbrushing Sucks - Radar Detector Jammer Forum
- lots of good, useful, info. and tips in these two threads