Good idea in concept but......
You have to be very careful in this application to get a foam with almost no expansion capability.
I have seen entire houses lifted from the foundation by overzealous application of expanding foam in every crack. It is not hard to imagine what could happen to a Burro
if too much was applied between the shells,it may end up like the Flintstone rig in the thread?
I have used the Hilti foam they sell at Home Depot and it comes in different expansion grades.
It seems to a higher grade product than the Great Stuff too and easier to control out of the straw.
For sure you want to try some in the thickness you are trying for on a test surface before going at the Burro
It is fun to use though!