One way to do that is by writing a custom Projection filter that queries all users by one or more selected roles.
Then add a Binding to the OwnerId property of the CommonPartRecord and create a Query that selects all BlogPosts whose CommonPartRecord.OwnerId equals a value from the querystring (e.g. ownerId).
Finally, add projections to your site that leverage these 2 queries.
So most of what you need is already possible, except for the filter that selects users by a set of roles (unless I'm missing something myself).