It seems impossible to me, because the url manager is bi-directional: creating URL and interpreting URL.
Isn’t it something you can do with the rules of the url manager? I mean, the rules for the frontend and those for the admin pages altogether in the configuration of the manager …
One thing I don’t understand is “security reasons”. I don’t think it could be a security issue. What do you have in mind for that?
And, another thing is a fact that we may sometimes want to create a front-end URL in the secured module, and vice versa. By switching url managers we have to use hard-coded url strings for those cases.
I think you could make a set of url rules for the secured module (and one for site/login) and position them before the general rules that generates language prefixed urls.
About “security reasons” I mean if somebody (like hacker) find the match pattern urlmanager roles for front-end system then he has the url’s pattern of back-end! Nobody want it! In contrast we want seperatly manage of secured modules (like administrator)
In addition I thing that is not very professional for a site to has seo url in admin or secured modules