Making it so registered accounts work on different directories.

Let’s say I have wordpress installed on example.com/news

Then a visitor makes an account on example.com/news and I promote them to a “contributor”

But I also have wordpress installed on example.com/media

Is there a way for the visitor to contribute to example.com/media without having to make an account there too?

Thanks in advance.

PS: If there isn’t a way to do it in 2.5.1 then is there in 2.6?