The amount of money you give to the airline has (fortunately) nothing to do with the kindness of the Captain.
The first contact is with the F/A, so be nice, don't put your fingers in your nose, make sure the person is not really busy with his/her job at that moment (otherwise he/she might forget your request or decide to disregard it because you pissed him/her off). Don't jump on the first F/A you see, that's probably the one who's in charge of directing the Self-Loading Cargo to their seats and he/she has something else to do. Try to locate one who doesn't look too busy and not too young, lock the target, make a big smile and go for it !
I wouldn't tell them you're studying tourism in France, that your family lives in Kenya, that BA cancelled the return coupon on your last flight with them, and that you're convinced someone is following you and wants to kill you, even though that would be a nice and very subtle joke that might make the Captain lough for decades.
:-)
Once in the cockpit, start by briefly introducing yourself. Don't expect anything, and tell yourself that they will kick you out in the next 30 seconds. The more you expect something, the more it shows, the less you might get it. Let them start the conversation, because you don't really know when they have a minute to talk, so they will chose themselves the best moment for them and they will be in a better "mood" to communicate with you.
Mmmmh, that's all I can say... I did that for years and it worked fine.
Good luck, tell us how it worked !