That sounds challenging! I recommend thinking of inventive way to "sneak" vegetables into your son's diet. He will grow out of this (although he may never enjoy anchovies!), but the repurcussions of his dietary restrictions could stay with him if he doesn't get enough nutrition. You should check out our regular columnist, The Sneaky Chef, written by Missy Chase Lapine. She has all sorts of ideas for sneaking vegetables, like pureed cauliflower, into kid-friendly dishes like mac and cheese. Here is the link for her column archive:
http://www.education.com/magazine/column/Sneaky_Chef/

I remember reading somewhere that the reason kids like such simple/bland food is that their taste buds are too sensitive- I think they called it hyperactive taste buds or something similar. Though that might be a big myth.

You may be interested in this new york times article: http://www.nytimes.com/2007/10/10/dining/10pick.html