Well I did what you suggested before you posted. I guess that is the best way to deal with it. For reference I have a Surly rear hub with an ACS freewheel.

The BB instructions said to have the 2.5mm shim installed if I have a 68mm BB (which I do) and then to shim as needed. I got another 2mm shim and the LBS was reluctant to sell me any more asking if I knew what I was doing (to be honest this was the first time I have done a SS and adjusted a BB for chain line so no) and asking if I had measured the BB once installed. With the added 2mm spacer (so the 2mm plus the 2.5mm that came with it) I believe the BB is centered in the frame (as best I can measure). I share the mechanic's concern to an extent and wonder (other than BB thread engagement to the frame which was his main concern) what the implications of shiming it over would be. Maybe I will try another 2mm and see what happens.

Thanks and anyone with any more BB shiming comments would be great.