Well slap me over the head, I was taking your URLs the wrong way around.
So to rewrite this: url.com/blah/blah/blah.php
Into: url.com/index.php?a=blah/blah/blah.php
Use this:
PHP Code:
RewriteEngine on
RewriteCond %{REQUEST_FILENAME} !index.php
RewriteRule ^(.*)$ /index.php?a=$1 [L]