1) the 'virtual drive' has a equivalent 'real directory'. That's what the mount command does, mount a directory as 'virtual drive' in dosbox.
2) you can use relative paths for your 'real directory' when mounting in the conf file. This works even on changing from windows to linux (if you use the '/' separator which works on both OS).
The requirement is to place the dosbox conf file on a directory 'near' the game directory (normally inside it or just outside) and mount the relative path from the conf file to the game dir.
A small primer in relative paths:
'.' is the identity operator - it means 'same directory as where we started' (in this case, the directory of the dosbox.conf file)
'..' is the 'parent directory' whatever it is named. It's not actually often needed.
'\' and '/' are path separators. Windows can use both, linux can only use '/'. So in relative paths it's better to use the second.
So for the 'discworld' directory, you could place the dosbox.conf file inside that dir and mount the game as:
mount c .. ==> means mount drive c as the parent directory of the dir that contains this dosbox.conf file; ie: it'd mount all of your 'Games' dir.
if you created a new directory 'Discworld' on your 'Games' dir and placed your conf file inside that dir, and created a dir named 'game' inside that is going to serve as a 'c drive' you could do:
mount c ./game
and install the game. You'd end up with a real path like Games\Discworld\game\discworld (this last from the game install) with the dosbox.conf in Games\Discworld
etc. It's not complicated.
edit: you probably also want to use quotes ('"mountpath") around the paths of mount, relative or not. They're needed for the path not to break the mount if it has spaces.