I will take some of what I have learned in teaching classes on poly to answer this one, too:

OK, so you know kink, right? You've been in it for a while and it's something that's important to you? Well, what's one of the central tenets of kink? The thing that separates practicing kink from just an interest, right? It's communication. If you've established a baseline already, I don't know from which side of the slash you're approaching it on, but your D-type/s-type deserves to know what you're feeling. How else can they share in the joy with you if they don't, right? If you've confided in your partner already, the hardest part is done! I know it's easier said than done, but if you keep in mind that one of the biggest joys of kink is performing it with people that revel in it with you, I hope it makes things a little bit easier.

I know this may be a sorta generic and maybe common answer, but I can go into the mindset even a little deeper and hopefully it'll help:

What do you enjoy about that side of your kink? What are you feeling when you're feeling wanty and want that time with your partner? Does your partner understand why it is you enjoy what you enjoy? Because you should share those feelings directly, both in general and when the wanty feeling strikes. This might allow your other side of the slash to read your body language or your temperment and help perform a little bit of anticipatory service on it. Really drill down with them into why you enjoy it if you can, be open and vulnerable, say, "it allows me to X and that's important to me because in my daily life, I can't do Y, or Y feeling can't be fulfilled," and that will help establish maybe a more solid baseline for you.

Again, I don't know which side of the dynamic you're on, but personally from my own experience, there is nothing that makes me happier than hearing a play partner confide in me when they have a unique feeling they want to feel in their life and they want to experience it through play. It's playing toys! Don't deny yourself or your partner from playing toys! It's a hellworld out there enough as it is, you and your partner deserve to feel good. ^^