Yes, why not

"You nod. "Alright. So do you want me to go to the bathroom real quick and see if the cage fits?"
Lydia smiles. "Oh, it will fit. And no, do it here."
"Really?" You say, looking at John, who nods. "I dont see why not. She´ll see you sooner or later."

"Alright" Still a bit unsure, you stand up, and open your trousers. Your hands shaking a bit, you pull down your pants, revealing your semi-errect cock to John and Lydia.
Before you know it, Lydia has a hand on your dick. "Holy fuck babe!", She looks at John. "Hes so much bigger than you and hes not even fucking hard."

Then she begins to slowly jerk you off and talk to you. "But you do seem to like the idea. Which thought do you like more, mmh? The thought of fucking me in front of John, making him watch? Or the thought of beeing locked by your best friends girlfriend. Maybe a bit of both? Either way, lets get you ready for the cage. Babe, you can watch, and see how it looks when a woman has a real cock to play with."
Then she lowers her head on your cock. You close your eyes, Lydia is incredible. Her tongue twirls around the tip of your penis, then she takes you deeper than most other girls managed. It doesnt take long for you to come close to cumming, which Lydia notices.
Kneeling in front of you, she jerks you off, while talking to you, striking the erfect balance between dominant and submissive.
"Please give me your cum, i want it so bad...cum for me...cum, so I can lock you up, and cage your cock, owning it: Please fill this sluts mouth with your cum while her boyfriend watches...fuck...your so big...."
And with a heavy orgasm, you shoot your cum in Lydias mouth, which she greedily swallows.
Then, before you know it, she grabs the cage, and forces it on your softening cock.
With a click, you´re locked.

"You look cute", she smiles, "Oh my god, this is gonna be so much fun!"