For some reason this has stuck in my head all day. Maybe Sage is making me a pod person or something.
It seems that if items are being bought for office use, the entire pathway is already accommodated in the PO system, including the use tax part of it.
But if items already in stock are being relieved for internal use, it seems that you could enter a S/O invoice (skip the order entry step if you like). Create a customer for the internal use. If necessary, create a sales tax code for use tax and assign it to that customer record. When entering the lines, change the unit price to equal the cost and change the G/L cost account to an expense account, ergo, Office Supplies.
This will create an entry to sales, A/R and Inventory. You want that inventory transaction but not the sales or A/R entries.
To resolve that, I'm thinking you can then enter a dummy payment through Cash Receipts and apply it to the Sales account. You may have to create a dummy bank code to make that work.
From a practical point of view, this is only workable if there are literally dozens of items, etc. to be relieved from inventory but theoretically, it could be workable.......