Some kids who hate highchairs are happy to sit at a child size table in a little chair. Perhaps it makes them feel more grown-up and normal. If you're not uncomfortable with using the tv as a tool, it may help if you allow the tv on while eating at first until he is used to the idea of sitting in one place - then you can phase it out.
Otherwise, you could try a booster seat, or pile of phone books, on your dining chair and wedge it between table and a wall for a bit of a safety/anti-wriggle factor - he may not like the feeling of being strapped in.
Like Jan said, being persistant and firm on whatever rule you decide on is going to help most in the long term. Easier said than done, I know. Good luck, hope something works for you.