Asap. Invite Gina over for dinner.

"Well, I don't know," I answered when my wife asked when she'd get the chance to watch me have sex with Gina. "I guess a better question is how do we get her to let you watch?"
"Oh, true, I'd not even thought of that... I don't want you sleeping with her if I can't be there to see it happen."
"Really? Why not?"
"That'd be too much like cheating on me. I know it's kind of weird but it feels like it's not cheating if I'm there too, you know?"
"Well, no, I don't, but okay," I replied, "What if we invite her over for dinner? We'll have to get a few drinks in her then to make sure she agrees... either that or we pretend you're out and you just hide in the wardrobe to watch."
"What?! I'm not hiding in the wardrobe. That's just creepy."
"Okay, so dinner and lots of wine just in case."
"Yes, then you just start kissing her while I'm out of the room. I'll come back and you just keep going while I sit beside you. You think that might work?"
"It could do. It's probably the best way. Just asking her to let you watch might not work so well.
"Good. I can't wait. I can't stop thinking about you and her. I want to be there to see everything. I want to watch you undress each other. I want to see you slide fingers into her, see her suck you, and watch you spread her legs and stick this beautiful penis of yours in her."
My wife grabbed my cock as she spoke, punctuating her desire by stroking me.
"It's so weird, but I want to see this spread her pretty little pussy open."
"Oh you will babe, I'll invite her over as soon as I see her at work. And then I'll fuck her for you. You'll just have to be patient until then."

Waiting until I saw Gina again at work was hard for me too, but really it wasn't long and she seemed excited if somewhat surprised when I finally did manage to get a moment with her to ask if she'd like to come for dinner after work. I immediately called Melanie to let her know that Gina had accepted and would be there at 6. "Oh fuck," she replied almost loud enough for Gina to hear, "I can't believe it's going to happen... I just felt my pussy twitch. It's so wet. I'm so turned on!"
"Yes, me too," I replied. Of course I wanted to tell her just how much I was looking forward to the possibility, but with Gina right there and us being in the office I couldn't say much more.

The day seemed to drag on, only broken up when Gina popped into my office, seemingly far more often than necessary. Eventually it was time to leave, and as Gina had insisted on ducking home to change and shower, after making sure she had our address and knew how to get there, I left to go home.