A standalone can only exist by itself, with with a VRRP backup with another standalone (which is purely there for backup, so everything is done on the primary).
You can configure an Master Controller Mode (MCM) MC with a 2nd MC. The MC would be for management only; you cannot terminate any APs to the MCM machine. I believe that the licenses have to be installed on the MCM, but if it is possible to do what you want, it would have to be in this mode, not standalone. You may try putting the AP/PEF/RFP and MC-VA-xx on the physical controller configured as the MCM, but again, the MCM could not terminate APs, so all AP traffic would have to be to the MC-VA.
Here are a couple of other threads from other questions regarding MM, standalone, and MCM where I have explained some of the differences between them.
https://community.arubanetworks.com/t5/Wireless-Access/Does-the-upgradation-to-Aruba-os-8-requires-a-mobility-master/m-p/509621
https://community.arubanetworks.com/t5/Wireless-Access/Arubaos8-two-controllers-redundancy-scenario/m-p/547580
I hope this helps,