How to keep content out of features?
Though I don't think this solves your problem of not wanting the content included in the feature at all, there are 2 ways that I know of to be able to create blocks that don't use numerical ids, and that can therefore be safely included in a feature.


Boxes
Beans


Personally, I prefer the Bean approach, since the Bean Bundles are fully fieldable, allowing to create very advanced types of blocks. Both of these modules however essentially allow you to create blocks that have machine_names (feature proof) as opposed to numerical ids, which as you know are a royal pain in the ass when it comes to features integration.

EDIT: actually, now that I think of it, Bean does not create blocks with machine_names - it uses numerical ID's. It is the Bean Types (think Content Types) that have machine_names. So, if you want blocks with machine_names, Boxes is the way to go.