Originally Posted by Brendan

Your cousin can use his miles to book in anyone's name. Or you all can do a Household Account simply by changing his address on his account to yours--as if he has :moved into" your home or apartment. Very plausible in these recessionary times--but they rarely if ever check.
But remember, each award booking from a HHA will withdraw miles from each account proportionally, so it's simpler to book awards from his account to use up most/ all of his miles.