Is there a delivered way to prevent requisition Line Defaults for Direct Connect Linked Suppliers?

Is there a delivered way to prevent Unit of Measure Line Defaults from overwriting the requisition lines for Linked Suppliers (direct connect vendors)? When punching out from a direct connect vendor's site, their unit of measure is passed back to PeopleSoft. The requisition is created with their unit of measure.  When the requester clicks on the "Requisition Settings" hyperlink from the requisition edit page, he can change the Unit of Measure line default.  Then the unit of measure of all the lines of the requisition will be overwritten.  This causes problems with direct connect POs because the Invoice coming back