WP Multisite using a pre-existing subdirectory install

Hi,

I have a question about a wordpress multisite using a pre-existing subdirectory install but “Site address (URL)” in root of the domain.

Is as it’s described in Using a pre-existing subdirectory install.

Somebody know the right way to make this?

I have this -> and want this:

http://www.mydomain.com/multisite/ -> http://www.mydomain.com/
http://www.mydomain.com/multisite/site1/ -> http://www.mydomain.com/site1/
http://www.mydomain.com/multisite/site2/ -> http://www.mydomain.com/site2/