Here's what I'd do... Played with beersmith for a bit and came up with......
0.50 oz Cascade [5.50 %] (60 min) Hops 9.1 IBU
0.50 oz Centennial [10.00 %] (60 min) Hops 16.5 IBU
0.25 oz Centennial [10.00 %] (30 min) Hops 6.4 IBU
0.25 oz Cascade [5.50 %] (15 min) Hops 2.3 IBU
0.25 oz Cascade [5.50 %] (5 min) Hops 1.8 IBU
0.25 oz Centennial [10.00 %] (5 min) Hops 1.6 IBU
Bitterness: 37.7 IBU (14.0-20.0 IBU)
At 75% efficency that'll give you 39.3ibu's of bitter AND!!! AND!!!! you will have more hop flavor/armoa because of the higher AA's of centennial. Instead of finishing with only .25oz of hops(cascade) you will be finishing with DOUBLE THAT AMOUNT!!! In the spirit of the brew It might be a tiny touch more of a hop flavor than most coors light people can handle but that other part of the spirit of the brew is to make a nice easy drinking beer with minimal ingridents to be enjoyed greatly by both being easy on the tastebuds and the wallet!