Can you select a Vendor on a Requisition which is not a Preferred Vendor of the Item?

My team is just getting on Requisitions. We have some items set as non inventory items for purchase set to hit specific GL account, and named after those accounts for convenience. When we only used POs we could choose any vendor at the header level and then enter these items at the line level. Now that we are starting to build out our Req forms, we see that at the line level, we need to choose a vendor from a dropdown which only includes vendors associated on the item record, which is none.

Looking for a way to get around this and still be able to choose any vendor with these non-inventory items at the line level. Do I really need to add every vendor to each of these items in order to make this work?