There are a couple of solutions here. Unfortunately neither are as simple as this ought to be. I think this is a good idea though, so I am going to submit it to Github ( where WC does its development )
The first option involves involves adding a meta field somewhere in the product date metabox and then using that value to toggle the
The status of
woocommerce_is_sold_individually is the condition that displays the quantity input on the single product page. True = hide that input and False = display the input. This is the development-side solution though, and I might even send them a pull request if I get a minute to fix it.
In the mean time you can override every woo template in your own theme. In your theme's folder create a folder called: woocommerce
Then create a folder inside that called single-product
Then inside that, add-to-cart
Basically we're going to mimic the folder structure inside the templates folder of the Woocommerce plugin files. Now go into the WooCommerce plugin files and find the file
COPY it. and then paste it into the
folder we created earlier.
Anything you do to the simple.php file nested in your theme folder will now be displayed in lieu of WooCommerce's version. (this is called Template Hierarchy by the way)
in your version (DO NOT HACK THE WOOCOMMERCE FILES!!) find the following:
if ( ! $product->is_sold_individually() )
woocommerce_quantity_input( array( 'min_value' => 1, 'max_value' => $product->backorders_allowed() ? '' : $product->get_stock_quantity() ) );
and delete it. The quantity input is now gone. The downside of this is that it is gone for every product you sell, which is why the development-side solution will be better.