One inventory item quantity to multiple divisions

That’s right, this is infeasible.

The answer to your problem is already in ideas.

However, for now you can do the following:

  1. For reporting purposes create a control account composed of special accounts to hold division-wise inventory allocations.

  2. Create sspecial accounts, one for each division (i.e. allocated inventory 001, allocated inventory 002, …) each assigned to its respective division.

  3. Create another special account unassigned to any division just to serve as a contra account in order to avoid double counting of inventory.

  4. At each reporting date, you can create this journal entry:

Account Debit Credit
allocated inventory 001 x
allocated inventory 002 x
contra account x

You can reverse the entry the next day or just before the next reporting journal entry to avoid unnecessary calculations.

This will ensure that your closed reports show the inventory values per division, while the total effect on your balance sheet is exactly Zero. (The control account will add up to Zero) and it shouldn’t show in reports without divisions.

However, for interim reports in between reporting periods, you will have to rely on inventory location report.