Hi,
It's quite easy to add. Create a custom product field with two values 0/1 and in the file "quantity" of the view "product" via the menu Display>Views, add that line at the beginning:
<?php if($this->row->column_name) return; ?>
where "column_name" is to be replaced by the column name of your custom field. And in each product you'll be able to configure if you want to display the add to cart or not.