Add feature to SelfControl software : choose network interface to block SelfControl is an open source software to block Internet connection for a time period. However, it blocks connection from ALL network interfaces. 
I'm looking for someone that would like to add a function in order to allow the user to choose the network interface to block. The goal is to block only the WiFi connection and let the ethernet working.
The source code is available at github.
Have you tried contacting Charlie Stigler or Steve Lambert, the creators of SelfControl? An offer to fund the feature would also likely help.

I expect you will get a better response from your enhancement request on the SelfControl issues page. More potential developers will see requests there and others will be able to back the issue to highlight its potential.