If he wants to get together with some folks who have a lot of experience organizing big rides in the area I would suggest contacting the Cascade Cycling Club (www.cascade.org). They do a number (at least 5 a year I think) of organized rides in Seattle and the surrounding area so they would know the ins and outs and what types of permitting, insurance etc that you would need - and could probably suggest good routes.

I'd be happy to pass the word around to the women's racing teams too to see if any of them would be interested in helping out.