as far as i know that cant be done ...
but thats only to what i know
maybe it could / can be done ... it will be diff to see apache vhost conf done via mysql backend but
you would still need to restart / rehash apache to get it to load the new sites / any changes that are made to the database conf file
so i done really see a point to trying to run apache vhost conf from mysql
.. just my pov on the topic sorry to be a tad down on it
as long as you tell apache to restart it shouldn't take any sites offline / any downloading file to stop downloading from your sites