Hello Rahman,
As given in above reply by Prasoon and Abu you can use the setting for any discount condition.
So by using RA01 condition you can achieve this , but get few things clarified by business.
1) is this commission amount is only for discount or credited to your company account.
2) if its for some other vendor then do they pay him via PO invoice if yes then you can use any freight condition copy to show the scenario of payment to different vendor,
3) if this is only to be credited to the commission account and then manual pay to vendor, then take a opinion of your finance guys as well
Thanks
Kunal