LDAP subscription access without local user creation

I am using WPMU LDAP plugin in my WordPress multisite installations without problems. Now there’s a need to create organization “internal blogs” which wouldn’t be accessible without LDAP-authentication. Problem is that I don’t want to start adding users (10000+ of them) to the local user database every time someone authenticates thru LDAP into these internal blogs, just for reading (aka subscription) access.

In other words, I need a plugin that makes reading the blog require LDAP authentication without local user creation for this cause. They’ll just gain subscriber priviledges to that particular blog until logout or cookie timeout. And only the blog writers would have a local user account in the WordPress user table.

Is there a ready, or near ready, solution out there or is someone interested making one?

[ Please do not bump, that’s not permitted here. ]