Communication is key, both verbal and non-verbal.
I’m sure that your wife is well versed in the art of subtle flirtation. A wandering gaze, eye contact, lick/bite of the lip, reaching across, closeness, touching, etc...
Also pay attention to his eyes, they tend not to lie. You’re likely to catch him checking out your wife.
As for verbal communication, I tend to find a way to steer the conversation towards the ls.
I may use the word “vanilla” to describe something or someone to see if they’re familiar with any ls terminology. You may even jokingly bring up the optics of the 3 of you having dinner together. This will certainly take his mind there, if it wasn’t before.
Lastly, I think you need to think about any negative consequences of him knowing that you’re into this ls. ie, judgement, outting you to others, uncomfortable further friendship/acquaintance, etc...
In my personal experience after feeling me out and mutual flirting, close friends, neighbors, etc... have just come right out and let me know they were interested, ie a cock/butt grab, wife calling herself a dirty slut, etc... These aren’t ppl that I work with or ******* go to school together so not much consequences and has never been a problem. At the very least I feel flattered.
Also fyi, if he isn’t experienced in the ls or is attached and open to playing, you’ll need to make him feel comfortable and zero pressure, else he may not be able to perform.
