variants Product Variants for Pre Order

Site URL: https://www.jenevoymakeupstudio.com/shop/make-up-for-ever-ultra-hd-self-setting-concealer

Hi! 

I have a client who has a number of different products for sale with variants. She wants to be able to offer pre-order on variants that are out of stock. Has anyone come across a work around for this? Below is a link to a product as an example. 

https://www.jenevoymakeupstudio.com/shop/make-up-for-ever-ultra-hd-self-setting-concealer 

Needing to change the "Add to Cart" button on only the variants that are out of stock.  I've create a pre-order work around on items without variants—see example here: 

https://www.jenevoymakeupstudio.com/shop/amika-perk-up-dry-shampoo

But this solution doesn't work when variants are involved because it requires that I change the "Add to Cart" button for all variants. 

Any help with this issue would be greatly appreciated, thank you!