Mary - are you aware of the HIV Vaccine Trials Unit here in Seattle? I'm in their volunteer pool, and Mimi's son has been a subject. They have a very cool website. I don't know if they would be any kind of participant in your rides, but you could mention the HVTU to interested bystanders along your ride if they want to do something to help with AIDS/HIV.
There are trials units scattered around the country, so interested folks you meet could probably find some way to get involved.
(the vaccine being tested now should be out for public use in 7 years. So far it works, now they are testing dosages and injection sites for the most efficient delivery method)
"If Americans want to live the American Dream, they should go to Denmark." - Richard Wilkinson