I've almost got everything sorted with my imports and the frontend to go public

What I need to do now is set default selection to a stockable custom field variant.
So in the frontend (please see screenshot) this means that instead of the product saying "select" for every custom field it actually selects a default config for that product.
The way this works is by adding a new variant to the product, selecting "Use current/parent product as derived" and filling in the required values (see backend screenshot).
This works great but I want this to be in my excel files that I import.
At the moment what I import to get the stockable custom fields in the product builder to work is by following the csvi manual on how to import stickable custom fields.
So this includes first import the stockable variants (VM products) with custom multiple fields (Y~Y~Y~Y...), custom title and custom value fields.
Then the actual products get imported marked as child product of the above product and all with their own custom title and custom value fields.
This all works fine but I'm struggling with is how to add that last variant to the product via import???
Maybe use a new import file and template somehow? but with what fields? Sorry I'm a bit lost here

Thanks, best regards, Ray