I believe DXo Viewpoint will help with this to a certain extent.
It not only straightens verticals, but has a geometric distortion correction that reduces the stretched look that extreme UWA lenses have near the left & right frame edge. Excellent for making the people on the edges of the frame look normal.
They just released version three last week...as a wide-angle lover I regard the software as a must have.
Capture One has a similar basic perspective correction tool that is excellent.
LR's implementation is awful on a couple of levels imo. I still use it if I'm confident my camera was level (because it's convenient), but for out of level shots, it's a disaster.



Should be here on Wednesday. 
