You need to man up

Logic tells you must act swiftly, directly.
Being assertive is what will get you Miranda, there's no other way.
The fact that you can't immediately dare her to do something to you, gets in the way tough.
It will require some minor sacrifices...

"Miranda, I want you to stop playing aroung with that fucking douche and come sit on my lap. You're mine for the rest of the night."

"Hey, chill out big man! She has to finish her own dare with me before of that..." Jeers Tom without even looking at you.

"Once I'm done with her, you can have her, I promise..." He grins confidently while at the same time giving a good squeeze to Miranda's breast to which she doesn't object.

"He's right John, you can't just ignore a dare in progress..." Hurries to add Nicole without showing particular interest in supporting either of your sides.

As she talks you know that everyone in the room is pretty much thinking the same, no need to check for a vote.
You perfectly knew things would go this way...

"Of course, I have no itention of bypassing the game's rules... All I mean was that I want Miranda to stop fooling around and get over with her dare.. Now."

You feel that your words have caused quite some sensation in everyone, you expected so.
Miranda looks the most surpriesd, almost shocked.
She stares at you with her jaw slighly dropped.
You see that she's even stopped jerking off Tom who, on is part, has not even noticed and stares at you as well, puzzled.

"W-What?"

"You heard me well, Miranda. I want you to make him come, right now. Stop pretending that you can't, I know that you can do it..." You reply dryily.

It's a bit of a gamble, you're well aware of that, but no one has to know about your doubts.
You must appear confident...

"Whoa, dude, thanks! I really appreciate the help..." Sneers Tom complely ignored by everyone.

The atmosphere is thick.
No one speaks, no one knows what to say.
Even Nicole is speechless.

"Ahem... H-How am I supposed to do? I mean do I have to...?" Stammers your crush with sparking eyes, face of bright red after a while.
She seems pleasingly compliant with your request and actually much more concerned about the practical aspects of your request than anything else.
Good...

"I don't know... I don't care, just remember that your pussy belongs to me from now on. Make him cum, Miranda, you have one minute." You raise.