Hello Dovydas. Unfortunately this won't solve my problem (I tested it). Odoo still counts the stock at the secondary location as available stock, which it simply isn't because my sales rep won't stop by the office until next week. So I want the products taken by the sales rep to be accounted for in Odoo (for insurance reasons), but I want it to be unavailable so that Odoo will not allow me to push a sales order with too many items on it. Do you understand what I mean?

It sound strange. I understand what you mean and tested this scenario in Odoo system and it worked. I created one extra internal location, then I receveid 10 products into main location, and 5 into extra internal location. When I as trying to sell 15 units I got a warning telling Not enough stock ! : You plan to sell 15.00 Unit(s) but you only have 10.00 Unit(s) available ! The real stock is 10.00 Unit(s). (without reservations).

I will have another look at it and report back here. Thank you for your time Dovydas.

It works now. The catch was that the new location couldn't have a parent location. When this new location had the parentlocation "Warehouse" it didn't work, but when I removed the parent it works. Thank you!

Just create sales person's location without parent location set. That way do not consider those location and stock of warehouse.