Not really following you. You can use the upgrade certificates for both you and the companion when traveling on a companion cert now. Two upgrade certs are required in each direction. This is explained right in the T&C's for the certs on the website. Is this not what you want to accomplish?

The T&C's can be found at the following page and section 13 on Transferabiliity mentions this specific case.

https://www.delta.com/content/www/en...-upgrades.html