My partner wants me to act jealous, but I'm polyamorous

I'm poly and comfortably dating a mono girl. I notice she likes to tell me about other people having crushes on her, and I always just say I can see why they like her and I enjoy the attention she gets. She knows I'm poly, but how can I lightly remind her that her interest in others, or other's interest in her doesn't make me envious without making her feel like I don't value her? We do talk about it, but sometimes I feel like I have to remind her without starting the big discussion again.

Well first off, are you fully confident that the reason she tells you this is because she wants you to feel envious? Unless you've explicitly asked her why she says stuff like this, and she said "because I feel loved and cherished when my partners express jealousy about other people having interest in me," my first advice is to find out where this is coming from. She could be thinking that because you're polyamorous, you like hearing that sort of thing; she could be trying to "meet you halfway" by talking about it. She could be trying out the idea of polyamory for herself in conversation, trying to see how you react.

But if you're sure that what she's trying to do is essentially bait you out of your polyamory and into expressing jealousy, it's okay for you to be more explicit: "I'm not able to do that for you - express jealousy or possessiveness." Then, ask her what she gets out of it when a partner talks and acts that way, and what you can do to make her feel valued and cherished in the same way without having to perform something you find icky or just false. 

Or, if this comes up infrequently enough, you could chalk it up to a compromise. Does it make her happier than it makes you frustrated? If so, might be worth it to just say something noncommittal like "well, but you're dating me, so if he's interested, that won't work" or "I'm glad I met you first, then" which acknowledges the monogamous nature of your relationship without you needing to perform jealousy. If you're able to expend the emotional energy, you could just leave it be as something she does that you would prefer she didn't, but isn't painful enough to warrant you trying to convince her to quit doing it.