PRE-ORDERS ONLY WHEN A VARIANT IS OUT OF STOCK

Site URL: https://www.urbanbasedancestudio.com/webshopmerch

Hi,

We have a limited stock cause we just started out and we only have a few items of each article.
We can order more any time and the waiting time is 2 weeks.
I'd like to be able to let customers know what size is in stock and which size they have to pre-order (=wait 2 weeks).

I found how to add the PRE-ORDER button, but that's for the article. It's either add to cart OR pre-order,
where I would like to be able for example to set Size small as add to cart (in stock), but Size medium as pre-order (out of stock).

Can anyone help me with this?

Did you ever find a solution??? Thanks!