Add a product without a price that can be added as custom as checkout

I use Square Space for my online store. I use Square Up for in-store purchases.  I am expanding my inventory and hours for in-store.

Instore, my inventory is pulled from Squarespace.  For the next few weeks, it would be really really helpful just to be able to have the option of adding a custom price without going through a product in inventory. I do have that option on Square Up, but it is set up with tax added. Ideally, I had a second custom button with no tax to use temporarily. I have both taxable and non-taxable items. I can not remove the tax from the custom amount on Square Up. 

It also is not an option for a second custom "button" on Square Up.

Is there an option to do that on Square Space or a clever work around?