Hiya @lemonsaurus and sorry to be slow to get back to you!
We do not have a wildcard branch feature right now; you’ve found the existing patterns:
- specify a single branch
- specify a pre-specified list of branches
- specify all branches
We’ll only build PR’s which target your listed branches.
So, how can you more granularly adjust what we build? Without a built-in feature, some customers (us included) use zaiper.com as a “middle man”, in production, and have for years:
- git sends all notifications to zapier.com. These notifications have a JSON body in a format that is reliably parse-able, and the payload includes things like the branch name!
- at Zapier, you’ve configured logic to do that parsing, and implement your desired set of “buildable-at-netlify” commits.
- you have Zapier “forward” (without changing!) the notifications for those commits, to Netlify.
This can be a bit finicky to configure for GitHub, since we don’t usually use webhooks to notify there, but if you aren’t turned off by the workflow let me know and I’ll talk through how you can get it setup. I can’t help with the code at zapier (ours is different than we’d recommend customers use), but that should hopefully be pretty straightforward - I am pretty sure Zapier “knows” GitHub commit notifications formats, and webhook “forwarding” is built in (cf Send new caught webhook data to another webhook).
We do also have an open feature request for making a real feature to do this, to which I have added your voice 
.