Dave Mayer sez:
Try it; set up the derailleur in the middle of the 7 cogs on your new wheel. That way, the cumulative error on the ends of the freewheel is less than 1mm.
This is my first choice, since it costs nothing and has worked (with reportedly varying degrees of success) for others. Beyond that, it looks like I have quite a few options.
Thanks for all the input - I appreciate it!