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You want Remote Buddy software + iRed software + the irTrans ir blaster + applescript.
iRed and the irTrans are sold in a bundle, for like 100 euros. Not cheap, but it gets the job done. iRed is very scriptable; it can learn ir button presses from your receiver's remote, and you can trigger those buttons through the ir blaster with simple applescripts, and tie those applescripts to buttons on your remote in Remote Buddy.
It's kind of a long chain of things to put together, but once you set it up it will work nicely.