Greed could suggest it pretty much any time you want to do it. He's's spoken to her just enough that he could just easily say "Gah, fuck explaining the meaning of life. Here. Let's go on log rides, eat habaneros raw and crowd surf. NOW do you get it?"

Greed's whimsical enough if it's fun he'll get himself in on anything, so, like I said, if you need someone to nudge Rei in various directions and no other character is available as a plot device, feel free to hit me at any time. Seems right now there's no particular need since others have stepped up to the plate!