Possible to use PO_CUSTOM_PRICE_PUB across multiple lines on PO?

I was looking at PO_CUSTOM_PRICE_PUB to use custom code for pricing on Purchase Orders…One of the requirements is to be able to do Tiered Pricing by item and after talking further with users have discovered it could potentially be across po lines…based on the supplier item number value. (i.e the items could be different but they will have the same supplier item number)

For example say the pricing is $2 for quantity 0-1000, but $1 for quantity 1000+
If line 1 is entered for item x, quantity of 500 and line 2 is entered for item y, quantity of 700, both have supplier item number z…then both lines should have a unit price of $1.