You should be able to add your custom repo near the top of the kickstart file, where the Fedora ones are located:
repo --name=custom --baseurl=http://server/repo/$releasever/$basearch/
This is based on looking at the kickstart file(s) in /usr/share/spin-kickstarts/
. I've used a similar method to 'roll my own' LiveUSB with additional packages (from rpmfusion). Which kickstart file(s) are you using for your VM?
P.S. I noticed your 'machine icon' too.