To show a set of products in a collection first regardless of sort you would need to customize the theme to show the gift certificates first in a separate loop.
Then choose whether or not to skip/hide those products in the regular loop though this creates pagination issues that need to then be solved.
To get this customization contact me at paull.newton+shopifyforums@gmail.com with this TOPIC, any other use-case details , store name and theme.
