Flexslider as default for Featured Section

I’m building a site that will have over a hundred portfolio posts to start with, all of which will use the Flexslider…

Is it possible to add something to functions.php or to the single-portfolio.php template that will force portfolio posts default to using the Flexslider in the Featured Section so I don’t have to check it every single time?

This will also make things simpler for my client to add future portfolio posts when I pass this off to them.

Thanks,
Eric