Well that certainly doesn't say it needs to be on the bumper OR that it cant be in the windshield, how about some suction cups? That would do the trick according to that.V C Section 5201 Positioning of Plates
Positioning of Plates
5201. License plates shall at all times be securely fastened to the vehicle for which they are issued so as to prevent the plates from swinging, shall be mounted in a position so as to be clearly visible, and so that the characters are upright and display from left to right, and shall be maintained in a condition so as to be clearly legible. The rear license plate shall be mounted not less than 12 inches nor more than 60 inches from the ground, and the front license plate shall be mounted not more than 60 inches from the ground.
(I don't believe there is any possible way to securely fasten the license plate to the windshield.)