We need to do a daily upsert of Pricing data from our quoting tool into the PriceBookEntry table in SFDC. Problem is that we cannot create a custom field in PriceBookEntry in SFDC, that can store the unique Pricing ID from the quoting tool, which can be used for the daily upsert process using Cast Iron. Also, we cannot get the PriceBookEntry IDs to be stored in a custom object, as you cannot write triggers on PriceBookEntry!

Has anyone encountered a similar scenario wherein there is a requirement for synchronizing the PriceBookEntry table between an external system and SFDC??