She can't go because she's "playing hockey?" Sounds like a tough chick.
Tell your "friend" not to stress about it. The more he texts her the more desperate he seems. He doesn't want to come off as too needy this early in the game.
Tell "him" to text her that's cool if she can't make it. Then at the party have him take a camera phone picture of something awesome happening at the party, preferably a picture with a bunch of girls and him in it (builds up the jealousy factor a little bit). Send it to her either that night or the next day, with a teasing message "you should've come

" or "you missed out

" or something to that effect. The smiley face really does wonders in text messages to take the potential cruel misinterpretation your words might have without them.
Then a week or so later, have him text her out of the blue and invite her out to something else.