HHonors has had this for some time, When you check in, mention that you have a car rental from one of the HHonors partners, and you should get bonus points from Hilton in your account. You may have to show your rental agreement at the time, although I've never been asked to show it. Also request additional airline bonus points at check-in, by asking them to put in an airline code (in your case "AA") next to the AB (for airline bonus) section in the computer with your reservation. The section for entering the car rental code on their screen is "CR", and they can put in the code for Avis for you.
Stayed at a Hilton in Fort Lauderdale two weeks ago, and got all the bonuses and points already posted to my Air Canada and Hilton accounts---11,566 to HHonors for a five day stay.

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'Tis better to have played and won, then never to have played at all.