Okay so last night I was at a club and had a HB9 on my arm and we walk outside so she can smoke.
Once outdoors I ask a another HB9 for a cigarette. She smiles, handing me a dart, as well as asking for my name, (social proof helped me here since I was already with a girl). We start talking and I sit down while gaming her. About 30 seconds into the conversation original HB9 asks if she can sit on my lap.

Now the point of gaming the second girl was to create jealously in the first one. I allowed her to sit on my lap, however, the other HB9 quickly lost interest in me after that. Which I guess is what the original girl wanted.

I think if I disallowed her to sit on my lap then she may have felt I was trying to act 'single' to get with this other girl or something. I wasn't really openly hitting on the other HB9, just playful conversation.
How would people suggest handling this situation in order to create maximum jealously in the target?

You don't need to overdo jealousy. You got her to persue you a little bit more, which is all you needed. Allowing her to sit on your lap was perfectly fine. Nothing wrong with that. If you had said no, then she probably wouldv gotten self-conscious (and not in a way that helps you) and it wouldv been worse. You did nothing wrong. Good job.

I agree, good job.

Thanks guys Yea thats definitely true. Saying no would have meant her standing there feeling weird while i tuned some other bird, definitely unhealthy. Thanks for pointing it out

You did perfectly well dude. As you already said: by wanting to sit on your lap, she expressed jealousy. She wanted to show the other girl a proof of possessiveness.
Basicly she told you, that your game worked.
And you don't need "maximum jealousy". She proofed that she was jealous, it's the sign you wanted.