I have two inch risers (ROX), on my bike and there is no problem with the cables. Rox suggest to remove the rubber spacer/washer from the casing that holds the cable into the frame. This allows the cable to be less taught and definitely is a must! When you pull the black spacer from the holder, it will sit on top of the original casing - this allows more freedom on the brake cable and should solve your issues.
"Men do not stop playing because they grow old, they grow old because they stop playing."
O. W. H.