With your own blog, you'll be free to emphasize the charitable aspects of your ride as much and in as many ways as you wish. Include a hit counter in the blog and a donations meter. Think up ride related contests to run on the blog. Have a bunch of cards along for handing out to as many people as you can. Leave them just laying around. Place ride notifications on as many web sites as you can.

CG is the world's premier bicycle touring site, but IMO, not particularly suitable for serious charity rides.