I agree. Know matter what, you have to be assertive. If you go in like, "umm... do you think that you could, uhh. give me some head... but only if you want to. It's no big deal", you will never get it. You might want to ease her into it by asking her to kiss it and then escalate it from there. Whatever you choose, be confident and assertive.
This just came to me... I think imma try it next time the situation comes up...
"He look... I think he likes you. Show him that you like him too... Give him a kiss."
Think of it as a form of
kino escalation.