I agree with Emm, this won't work, he wants to hurt you and he is using other people to do it, this is SO far away from what poly IS (and I don't think anyone would disagree with that particular generalisation!
He cannot use others just to get back at you and you cannot allow yourself to be used that way. If he is too immature to forgive you without this destructive behaviour than you are probably better off without him. He just wants to cause you the same sort of pain he felt but it is BS I am afraid. Cut your losses and tell him to sling his hook and enjoy the look on his pathetic weasly face when he realises you have called his bluff and taken control back into your life!