many of my relatives who fly do not care about miles (gasp indeed!) so what I do is this:
1) I try to buy their tickets on my mileage earning CC and have them give me cash for them.
2) When they earn miles--and I basically just sign them up for them and tell them to provide the number at check in--I make sure this gets done with a promo or in conjunction with some offer if possible. For example, refer a friend with UAL or some email sign up thing or something...
3) I manage all their accounts and if they ever really DO need something, I gladly give it to them, noting that it is THEIR account not mine. Sure maybe this does them a favor on my time and effort but hey, that's what friends and family are for! It all comes around.
4) I keep the accounts up to date like making sure they do not expire, etc. I can even do mall purchases to make this be so. I keep a file that tracks everything for me and hey, one day one of them DOES come callin and asks about miles (One relative bought tix to Australia and suddenly they were interested and since they had the 8k miles I saved for them earlier on in life, this added up to a free ticket to anywhere in the US at 25k! She went skiing in Colorado because of this and guess who got the case of fine wine at the next reunion?!)
5) If their accounts reach level--or in the case of some airlines, reach some amount that can be transferred for a fee, then everyone kinda wins.
6) I have even used the UA miles some relatives have received to get restaurant.com gift certs and then donate those to our church and get tax write offs!
Again in every case, I am telling these relatives what I am doing so no one gets pissed off. It's amazing how once something is worth something, that people do change.
DO NOT, however, let people NOT get miles.
Them's just my tips for the day. GO RED SOX!
they won their opening day game in Japan!

MM