See what Jürgen put. My suggestion is just using Storage Locations to get the right address on the PO and so you can see stock by SLoc but the cost all goes to the CC for the main dept. at the time of GR as the stock won't be valuated (and possibly adjustment amounts at time of invoice).
They're not really dummy SLocs as they represent real locations with stock (though you would normally have SLocs defined under a Plant that were on the same physical site).
My understanding was material was delivered direct to each Sloc. but that may be wrong (?)
If delivered to a central point and then moved to main dept. locations you could use Sloc to Sloc scenario to generate necessary paperwork but it's all under the same Plant.
If you want to charge on GI to sub-dept. i.e. after stock delivered to main dept. location from the central location, then better to have valuated material i.e. stock account credited on initial receipt, then GI to sub-dept. and define sub-dept. CC at that time.
You'll be able to see which Sloc has how much of each material. You'll have material held against a stock account until that point so you've got stock held as company 'asset' for GL purposes. Provided stock doesn't spend too much time unused and it's not especially valuable it should be an acceptable solution. It's a central stores, transfer to regional stores, issue to ultimate end user dept. and hit sub-dept CC at that point situation.
You can either hit a CC at GR (consumption) or on GI (stock account and subsequent GI) but not when material transferred from one Sloc to another.