I think I've got the LR4-to-CS5-LR4 down pat, and can now soft proof in LR4 on a virtual copy. Also, no problem printing from LR4 from the soft proofed VC.
For a number of reasons I still prefer to print from Qimage. So far what I have done is to export the soft proofed VC as a flattened tiff, which works in Qimage. What I would like to do then is delete the tiff file yet leave a soft proofed VC, which doesn't take up disk space but would be readily available to use again.
While I have some 12 years of Photoshop experience I'm still easily confused by how things happen in LR4, so pardon me if the obvious solution is staring me in the face