I did the following:
1. Burn the Budgie/Gnome/Mate iso to a USB stick, I used dd to do it but whatever works is fine
2. Booted the system from the USB stick, in your case boot the VM from your iso of choice
3. Wait around a minute or two, hit alt F2, you'll hear a sound if oyu hold backspace, type terminal and hit enter, then type orca and hit enter, it'll start Orca
From there it's an easy to use installer, the only part I had isues with was the name/username bit but I used the same name for both.
Once I had it installed I didn't restart immediately, I went and tinkered around to set the defaults up how I want, then restarted and just a heads up....by default, it'll ask for your password but you an easily enable auto log in once you're at the desktop and Orca's started up.
There you go, hopefully that helps. I've been talking with the Solus guys about Orca actually and they have been very helpful with helping me with a few minor issues, so credit where it's due.