That's more of a BOINC question, since they are the ones who develop the framework the projects use. Such a feature would not be effective here until it were implemented at the project level. For now, the best you can do is to "obscure" your account, but ultimately the adage applies that anything put on the Internet will stay on the Internet, forever. There are enough stats sites and page caching by search engines, that someone could find that you were active with BOINC--if they REALLY wanted to. But, why would they want to?
You're not the first to ask for such a feature, but I've never really gotten a sense of why you'd want to disassociate yourself with BOINC... Aside from being a thoroughly nerdy endeavor, are you afraid someone will find out that you helped to process research in search of disease cures, or astrophysical data?
