Press F9–c–e and then add something like:
[doom-quake-idsoft]
Regex=\\.pk[34]_?$
RegexIgnoreCase=true
Open=%cd %p/uzip://
View=%view{ascii} /usr/lib/mc/ext.d/archive.sh view zip
The section name doom-quake-idsoft can be changed to taste. This edits ~/.config/mc/mc.ext.ini, the other relevant file is /etc/mc/mc.ext.ini.
// Oliver
PS: this also recognizes the files if the extension contains a trailing underscore (_), which I use to deactivate individual mods, sometimes.