Beryl- Sounds like an all round crappy situation. Since you already know your boss isn't a big fan of the Witnesses, could you maybe explain that you are an Ex-W and the issues and uncomfortableness sitting next to this guy are causing you?
I had a similar situation at work awhile ago. I work at an Indian Casino in a bar, where you'd think you wouldn't run into this issue, but my bar is attatched to a restaurant. The casino hired a bingo bus driver who was a JW (I know ??!!) and since she did not gamble, she would spend her time reading propaganda literature in the restaurant at the table facing my bar and would "witness" to the servers. I on seeing the situiation made it a point to "shout loudly and proudly" that I was an ex-jw to the waitstaff, which led to a lively conversation on JW beliefs and why this crazy bat was trying to give them magazines. Soon the waitstaff was pointing to me in the bar when bingo bat lady would try to give them magazines or preach and explaining they didn't want to take her magazines. She moved tables and quit preaching, problem solved!