How can I merge two size filter groups into one?

I have a slightly odd requirement and I’m hoping someone can help point me in the right direction. Essentially my client is using filters and for various reasons they have ended up with 2 filter groups for Size, one driven by metafields and one by variations. They need to keep the 2 different ways of applying Size, but they want me to merge these 2 groups into a single Size filter group, so that collection pages have just the 1 group. Does anybody know if that is possible and how to achieve it?

Thanks in advance

Dave

It looks like the merged value feature that you can use in this app https://apps.shopify.com/ultimate-search-and-filter-1. You can merge different values like Blue, Light Blue and Dark Blue into Blue.

Did you ever find a solution to this? I am having the same issue. Thank you!