It would be a shame to not be able to use those wheels. They look great.
American Racing does make a 15x8 with a 5x5 pattern and 4.5” backspace – part number A695873 in the Ansen Sprint series. Not sure if the extra inch in width would still cause a problem on the fender side or not.
http://www.wheelsforless.com/detail.aspx?ID=2520
They also list a 15x7 with a 4” offset – part number A695773. Perhaps if you could find the new wheels on sale somewhere they might cost less than swapping the rear axle.