I actually have two separate but related issues.
I've never received a response to this question in the past.
What I do is build my own ribbon panel with the commands in the order I prefer as shown below.
It's a workaround, but easy enough to setup.
An alternative would be to customize the Marking Menu to make Place From Vault & Place from Content Center availale as shown below.
This is quite easy to do, simply customize the marking menu.
Gentlemen,
Thank you both for your suggestions. I added the Place from Vault button to my ribbon as suggested. However, I'm going to hold off on accepting either as a solution, as both of these are workarounds (albeit good ones!). It would be great if the apparently intended functionality of having the button be stick on the last used function actually worked.