He also gets some other benefits by just holding the card....

If you really wanna do this:

Have him open the card and help him meet the minimum spend by paying him back cash for goods.

Then when the bonus miles hit, bring the $450 + your agreed upon price for 100k miles, sit in front of a computer and say "Ok transfer them to my[BA/DL/whatever] FF account and I'll hand over the cash."

You're not out any cash until you get miles.

If you do it quickly you could get 150k BA. In fact, he could advance 60k points the day he opened the card to make sure you get most of it out during the bonus to BA period.