you may not be aware, but you can cache public folders in your OST file.
This can only be done for public folder "favorites", but such would allow the drag-drop to the PF occur locally, and then the OST sync threads in outlook would handle the push up to the PF.
I'm not aware of an easy way to automate this change for outlook however, so you'd still have to train users on this option. but such could likely be done with a few screen shots:

public Folder favorites are done by dragging folders to the "favorites" area above top of the folder tree in outlook.
-Eriq VanBibber, CTO, Priasoft Inc.