I see comments like that every once in a while, and I always come back to something that one of my professors told me a long time ago. If it took you like five minutes of thinking about it to come up with it, it's a safe bet that a) folks who are paid to work on this stuff full-time have already thought about it and b) that someone already figured out how to work around it.
That's great if you're looking for whole extra boards in a device with grams or tens of grams of additional mass.
These surface mount components are so small that the variation in the volume of solder on the joints alone would render your technique moot.
Add to that, the fact that manufacturers often use multiple suppliers for parts, they could have different materials, densities and casing designs, this particular problem is beyond weighing.