The simplest method without using a frontend would be to copy DOSBox to the same directory as daggerfall so that the dosbox.exe resides in the same directory as the daggerfall executable.
Generate a new dosbox config file with the name dosbox.conf
Add your lines to the autoexec area in dosbox.conf (with changes to the paths)
Create a shortcut to the dosbox.exe that is in the daggerfall folder.

You can also do the above without copying dosbox to the game folder using a seperate config file if you want and just have dosbox load the extra config file.

Just add these lines to the end of DOSBOX.CONF, in the [autoexec] section.

If your brother also uses DOSBox for other things, and you do not want it to be in the general configuration file, just create a copy of the file, then put a shortcut on the desktop to run DOSBox with -conf <config_file> argument.

^^ Looks like I was beaten to the punch ^^ 🤣