You can use squashfs to import large amounts of data into a guest. First you prepare the squashfs image:
/sbin/mksquashfs data [...] data.sqsh
and then you can add it to the guest as an extra data
drive. In the example below, we show how to make a
squashfs from the contents of some local directory
/usr/share/man/man8 in this example)
and then make that appear in the guest.