minimum lot charges for PO's

version 6.1

how do you generate a po for an inventory item where a minimum lot
charge applies? for example let's say we're going to send out 150 parts
to be plated and the op cost in the routing is $1.00 each. if we write
to PO it comes out for a total PO  cost of $150. 

but suppose the vendor charges a minimum of $200 to heat the plating
tank. he is going to charge us $200 to do the 150 parts. how do i
reflect this on the po so that the vendor sees it and so that the a/p
people see it?