Restricting people picker users to 9 OUs

We have 9 OUs within our organisation that contain the entire user base. I want to set the people picker to pick up only the users within those by the 

Set-SPSite -Identity <url> -UserAccountDirectoryPath "OU=OUName,DC=xxx,DC=com" command.

However, I am only able to specify one OU in the command.

And doing that prevents NEW USERS in other OUs from having access to our intranet site. I have to then run the above command with that particular OU.

Is there a resolution to this? Did not find any for the multiple OUs command.

Thanks in advance

Srinivas