Loading BP and BP Relationships!!!!!!!!!

dear SDN friends!!!

I am in a dilemma please help me!!!!

We are loading BP in our system from a flat file. I am using LSMW with CRMXIF_PARTNER_SAVE for BP and CRMXIF_PARTNER_REL_SAVE for BP Relationship.

My problem is when loading BP relationships i have to provide LSMW the partner numbers for the relationship where i have a flat file which depicts BP number according to their legacy system with their partner numbers and so on

when the BP comes in SAPCRM it has a different number which is assigned by our system config. Then how do i distinguish which partner number has relationship to which partner?????

Please provide your valuable advise to help me go through with it!!!!!!!!!!!

Pankaj