This gets much harder if you have a family and all want to opt out. Of course, a crying or annoyed kid usually provides sufficient motivation to TSA to not keep you waiting as long as you stay courteous (as much as possible given the conditions).
Last time my family and I went back to Europe, at Tom Bradley International Terminal at LAX, our family was directed to a special families-only line, which didn't have full-body scanners at all, and didn't even do pad downs - just went thru the old-fashioned metal detector and X-Ray for the carry-on luggage. We were pleasantly surprised as we were expecting the old nightmare.
Traveling with my kids has been easier (in this regard) because the family line doesn't have the full body scanners at any of the airports I've been through (Atlanta, Chicago, Dallas, Houston, Denver, Seattle ...). Traveling alone I usually have to opt out, though sometimes one can choose a line without a scanner.
