How to use #DigiKam without importing everything into `$HOME`?

I don’t have the hard disk space on my primary drive, so all of my media is on a separate drive. I want to keep it that way, yet still use the facial recognition functionality.

https://mail.kde.org/pipermail/digikam-users/2009-September/008288.html

showfoto doesn’t solve this, but it is a powerful image viewer.