For example you have an upsell page with 2 or 3 columns, describing different options or packages of your product, and each column has a "Buy now" button. But you have only 1 variable product with 3 variations.
What you need to do in this scenario:
You need to append your selected variation attribute(s) to the [wc_1cu_yes] button in a format like this:
You can get the NAME and the VALUE from the select boxes on the product's page.
For example, Special Delivery options:
Only CDs: [wc_1cu_yes]&1cu_attr=attribute_pa_delivery:cds
Only MP3s: [wc_1cu_yes]&1cu_attr=attribute_pa_delivery:mp3s-only
Both MP3s and CDs: [wc_1cu_yes]&1cu_attr=attribute_pa_delivery:mp3s-and-cds