Mmm. I'm not an expert on SRAM GXP. I'm thinking that you could install a ~2mm spacer inside at least the drive side cup to space the crankset over a little bit. I don't know if that'd offer you enough room or not. If not, then I'd say you may need to consider either a smaller chain wheel or something like a square taper crank where you can tune the chain line a little easier (with different length spindles).