Just do it.
Send out an office wide email on Monday that says: Look, we know some of you folks blog. Sure, you haven't told us so, and no we're not monitoring your site surfing (much), and no we're not mad at you for doing it. Actually quite the opposite. As a company, we'd like to understand more about blogging. And we want you who are already blogging to tell us. You're the experts. You understand the space. So, let's have a lunch and learn session next week. Pizza is on the company and everyone's invited--just bring your blogging knowledge and your favorite blogs (or at least the ones you think the rest of us should be reading) and let's talk about this blogging thing. If you would like to be one of the blogger hosts for this lunch, email [[insert your email here]].
[[insert your name/title here]]