Auto change of conditon price during MIRO Posting.

Dear Experts,

The scenario is  business purchases the goods from a secondary vendor on commission basis and pays the actual amount to primary vendor but commission paid depends on some percentage of the amount paid to primary vendor this commission will not be same during invoice posting  as amount paid to primary vendor changes so as secondary vendor how this commission calculation can be mapped during Miro posting.

Thanks

Vijaya Rebala