My guess is it's not implemented into the blog module yet! The blog module would need to setup an owner or something like that! Maybe you should contact the blog module developper to ask him to integrate that into the module!
You can setup who can look at a page and edit it but it's only from and relative to the CMS side that this control can be managed. You cannot prevent a blog engine from allowing a user to post on one of more blog engines. If you want to setup this as a normal SS CMS based operation, then you will have to generate a section for each user that you'll call a blog page (not a blog module) and configure each user manually to be able to edit their specific section. Then all pages under them will inherit the same settings forcing only the configured user to edit the pages in question.