upstream of pam_mount pointed me to OpenSUSE's gpg-offline RPM macros at
They allow to use a keyring and detached signature as additional source
in SPECs to get both verified. Since gpg-offline's upstream is willing
to create a proper release to allow easy packaging for Fedora, I wonder
if I will find any obstacles when I package it. The packaging guidelines
allow packaging RPM macros, therefore this should be fine.
Also I am interested whether there are better options available.