You can leave it as it is and mount the cowling as far as possible forward with enough 'flesh' for the screws. You will simply have a larger gap between the spinner and the cowling and you might have to mount the battery more to the back to get the plane balanced well.

Tomorrow I'm going to purchase the Edge so I can't tell how the firewall looks like, but it's also an option to cut, in your case, an half inch of the firewall with a tenon saw. See attached image. I did the same with my Funtana because I had a Saito 150 installed. I glued 2 pieces of plywood together to get the right thickness for the 8-32 blind nuts, put some triangled wood in the corners, glued eveything together with 30 min epoxy and finsihed it with varnish.