Nah, it is to ensure 100% that if a nut comes off the control arm won't fall out (an exaggeration, but I bet it's right there in the FMEA as a high severity item).
To do it the right way, $400 doesn't sound that unreasonable. Many shops would be uncomfortable with the "upside down" bolt method, liability litigation being what it is today. Depends on how well you know the shop owner.