Is there a way to disable the combined files option so it is easier to create a custom theme?

I've created a custom theme folder etc as the in the quick demo.

combined files are great for he end result but not so helpful when developing.

I always thought Director set_environment_type('dev'); would disable combined files? thats what it says in silverstripe 2.4 book

i usually use expresso.app which allows me to quickly select class/id elements and map the css path to local files etc.

When they are combine this obviously causes an problem.
It would be great to be able to see the css structure rendered in the source. so i can see what css files that actually need editing.

I have commented out SilverCartPage.php line 281 to 320 temporarily which seemed to fix it

unless there is a better way