Jeff looks up (down?) at his cock, already hard and pointed at him. Then he looks back at his strange figure in the mirror. Then he gets an idea and smiles wickedly.
Jeff goes over the command in the Chronivac once more before excitedly hitting enter. The first changes are more subtle this time, fusing his tongue and teeth to the inside of his mouth. His lips lose their definition as his mouth begins to get bigger and tighter. His head quickly turns right-side up as his hair and other facial features start to disappear. His head begins shrinking while his neck begins getting thinner. His mouth is now at the center of his face, and despite not having any other sensory organs, Jeff can still see, smell, hear, feel, and taste. His mouth is shut vertically and he can't seem to open it. His chin splits, making the two sides of his swollen head more pronounced. His neck is about 4 times as long as his head, with a vertical line of skin starting from his chin and going down. Jeff stares in awe as his transformation ends with his nether bits up near his arms disappearing.
Jeff steps back from the mirror and looks at what he has turned into. There, in his reflection staring back is his own erect cock head. He reaches down with one hand and feels along his length. It makes him even harder. His own face is now nothing more than a long cock. His month's only purpose is to expell seed and urine. It feels amazing.
Without hesitation, Jeff begins rubbing his hands all over his "face" and "neck". It all feels incredibly sensitive. He loves the way everything looks from his perspective. The blank expression on his cock head staring back at him almost looks cute now. A bead of pre forms on his lips, adding to the effect. He feels right at home between his own two legs.
Soon enough, he can't take his load anymore. His mouth is forced open for a moment as his neck tightens and sends hot, white cum spewing out. It tastes amazing.