Deactivate buy button until product variation is selected

Hi,
Great little plugin – just what I was looking for!

However, when using it with product variations the button is active when no variation has been selected. If you do click on the buy button without selecting a product, it takes you to Checkout with the first available variation added to the cart, which is confusing for the customer.

Could you change the Buy Button behavior to match the standard product variation add-to-cart process where the buy button is deactivated (i.e. grayed out) until a specific product variation is selected?

Many thanks in advance, and as I said great little plugin!