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.