fixing CA

I've taken a shot of a church, with the church far too dark; I tried bracketing at the time but didn't have a tripod at hand, so combining multiple exposures is out, as they will not line up.

I played with the brightness in DPP (shot raw) and created 2 tiffs, one pulling out the detail of the church and one preserving the highlights in the clouds; however when I try to combine them I'm getting a lot of CA from the overexposed version, around the edges of the church where it meets the sky.

only way I can think to fix this is to go round the edges and carefully de-sat red and blue using a quick mask. any other ideas?

Using ACR on the 3rd tab there are correction sliders for CA - if you cannot use ACR try looking at the adjustment settings for DPP - they may have a correction element similar to ACR. This way you can control it even before you open the image.