And So I have this code developing a "fake directory"

Options +FollowSymLinks 
RewriteEngine On

RewriteCond %{SCRIPT_FILENAME} !-d 
RewriteCond %{SCRIPT_FILENAME} !-f

RewriteRule ^(\w+)$ ?username=$1 

However I would like an imitation subdirectory by using it, e.g.

profile/johnsmith/photos

which will Rewrite to

?username=johnsmith&tab=photos

EDIT

I've attempted

Options +FollowSymLinks 
RewriteEngine On

RewriteCond %{SCRIPT_FILENAME} !-d 
RewriteCond %{SCRIPT_FILENAME} !-f

RewriteRule ^(\w+)$ ?username=$1&tab=$2
RewriteRule ^(\w+)(/(\w+))?$ ?username=$1&tab=$3