I don't suggest it. It's not in my wedding planner.
However, I have been party to this "custom."
If the B&G choose to have it, then I always tell them that should a child be involved, the "garter" will be placed on the arm of the female...not leg replacement.
There are a couple of ways to do the Garter/Bouquet toss. I remember doing the "circle pass" of the Garter/Bouquet as another way to avoid the "leg placement."
Two circles. Inner circle are single females looking at B&G who are in the center. Outer circle are males with backs to the inner circle.
Garter is given to the "outer circle" and asked to begin handing it off in one direction. Bouquet is given to the "inner circle" and asked to hand off in the opposite direction of the male circle.
When music is stopped whomever has the Garter and Bouquet are the recepients. This method does allow for a specific person to be chosen in advance to receive the Garter or Bouquet. The DJ must really keep eyes on where the Garter or Bouquet is at all times so that when the music is stopped the "chosen" person is in fact receiving the Garter or Bouquet.
It can be hiliarious and surprising. I remember one wedding where there was no specific person selected to receive the garter or bouquet. As it turned out the male and female who ended up with the the Garter and Bouquet were an item and had been dating for several years. The were married a year later.
So, for those seeking another way around the "replacement" issue, there you go.