I’m not actually using a select, each option actually has its own buy now button:
{boards}<li>
{exp:cartthrob:add_to_cart_form entry_id="{entry_id}" return="cart/index" show_errors="yes"}
{!--{inventory:reduce entry_id="{entry_id}" quantity="1"} --}
<div>
<input type="hidden" name="item_options[boards]" value="{option_value}">
<button type="submit">Buy now</button>
</div>
{/exp:cartthrob:add_to_cart_form}
</li>
{/boards}
