You can always go outward--I had my rear quarters pulled out by a shop (required repainting) 1 1/2" per side. It kept the Hoosier A6 315's tucked in there nice even with the 18x9 rim
Those tires are WAY to wide for that size rim. I bet you could get the same amount of traction with a 275 because the contact patch will be better.
2003 Corvette Z06 - MGW shifter, Corsa X pipe, Corsa Xtreme exhaust, Texas Speed long tubes w/o cats, PowerStop rotors/pads, Conti DWS tires, C6Z51 F&R sways, C5R headlights, tuned
04 GTO - sold