I did have the same problem with my little brother about 3 years ago, but it was just a case of giving him Minis to paint, for instance, i let him have control of all the Mordor elements of the army (all the orcs, captains, you know...) and then i just let him hand pick figures out of my collection to paint, he's not exactly brilliant so i let him paint dwarves seeing as i have no interest in them.
Another thing is, if you have any other friends playing the game, invite them over to your house or meet somewhere for a game, but let you brother watch, he will soon realise what he is missing, then just leave him the rulebook to look at when he's by himself, and before you know it, you should have a regular gaming partner!
By the way, carrying on from UKFB's and Burning Mithril's suggestion, if you can play SBG then i would definatley reccomend introducing that to him first, so you can start with small skirmishes and slowly increases the points, then when you think he is ready, ask him if he would like to take the jump up to WOTR.
Good Luck!