Are you having bridesmaids? Could he walk down the aisle with them looking cute?
I don't think little ones need to have jobs to be involved in the wedding party - just being there for cuteness reasons alone is enough!
My OH's little brother will be 6 when we get married - I plan for him to walk down the aisle with our flower girl who'll be 4 - they can both scatter petals, but I think this is enough responsibility for each, and I don't think either would be asking why they didn't have a job if they weren't in charge of petals. Both currently know we're getting married and they will be there as flower girl/page boy, but neither know what these jobs are or what they involve, so we're completely free to decide what they do/don't do! I'm pretty sure just being given a special outfit will make them feel special and involved.
Flower girls little brother will be 2 by the time we get married - everyone has varying opinions on how involved he should be. I think he should be there looking cute and smart, and he can decide if he wants to go down the aisle on the day or not, but I think this would be enough of an achievement, without giving him a job!
Not counting the days to 14th June 2013 out of denial - I'm going for the least-organised hitcher award