If your company booked you into J and your co-worker into Y, then you (and especially your co-worker) should discuss it with them.

If the company booked both of you into Y, and you upgraded, then you knew when you did that that you and your co-worker would be in different cabins. Live with it. Visit before you get on the plane and after you get off.

It is very inconsiderate (IMO) to stand in the aisle visiting with someone for a half-hour or an hour. If it is all that important to you, ride in the back with him.

Of course, if you just want him to visit you in J so he can be impressed with how smart you are for figuring out how to get in J, buy him a copy of the Seinfeld DVD where Jerry is in F and Elaine is in Y. He will be much more jealous this way.