Boot Windows from USB with EFI password
What you are asking for is not a common configuration. I can confirm my answer works on my 2011 and 2013 iMacs running High Sierra and Mojave. I can not guarantee success on a 2013 MacBook Air running El Capitan. You would have to try the solution.

The basic steps are given below.


Allocate space for new small partition that is FAT formatted.
Install rEFInd in this new partition.
Edit refind.conf to configure rEFInd to add boot options for Windows and macOS.
Add a Startup application to macOS
Add Startup application to the dock. (optional)
Launch Startup application to select default operating system. 


An example of the Startup application is shown below.

 

You can install rEFInd in a small FAT formatted partition  and application on