Do you invest, advise or other ways involved with any co.s that choose not to participate in YC or have matured beyond a YC stage? Some startups need more your sage advice, than any investment.
If I was in your situation and my startup closely aligned with pg's interests what I'd do is find a mutual contact who pg trusts and will give you a rave introduction.
For that matter the same applies to any other investor.
Honestly you are probably better off doing YC around when you'd do a Series A, or even slightly after, assuming all your investors would be ok with it (they should be), vs. really early.
But in answer to your question, no, except for one startup from Imagine K12.