So I figure out how to do it. I had done something similar to what you did Glitterati last time, for some reason that wasn't working for me today. So here's what I did:
I loaded in the Shoes at their default for Luna with the Bows parented and in place. Because I needed something slightly different for each foot so that they would be placed correctly, I selected one of the bows and in the Parameters Palette chose Create New Master Parameter
I named my new parameter Newborn. In the window that popped up, I clicked Start Teaching, and I set the Scale and all the rotations and translations the way the would need to be on the default.
Then I clicked next key, and set the value of the Parameter to 1.0. I then set the Shoes Newborn morph to 1.0. I went back to the bow, and adjusted the scale and the position until it was correct for the newborn morph, then clicked stop teaching.
This was all done in the Keyed Dependencies tab. I then went to Value Operations, Created a new Value Op, and selected the NewBornBody morph on my shoes. I had to change the Scale Factor to 1.0.
Did the same thing on the other bow, and it seems to be working.
Okay, to be fair, I didn't do it quite that straightforward or in quite that order. But, had I known what I was doing from the beginning, that would have been the way to do it
Seems to be working, and pretty soon I'll be ready to have some other Poser users test out my shoes, so we'll see what happens then.