How Can I Set Default For Resource Attribute in a Template

I have a WayFinder menu that regards each submenu parent as a category only.

For these documents I'd like to create a non-content template that:

1) Includes a call to FirstChildRedirect snippet.
2) Presets the Link Attributes resource field (link_attributes) in the document to

Number 1 is easy.
How do I do number 2?

Thanks in advance. [ed. note: dwayne last edited this post 11 years, 7 months ago.]