Unrar at V4+

My Cloud OS 3 Personal & Network Attached Storage My Cloud
4

I installed omv and it works there.  http://community.wd.com/t5/WD-My-Cloud/Clean-debian-and-OpenMediaVault-on-WDMyCloud/td-p/785505

but i want it on the mycloud firmware. does anyone know how i install unrar at firmware 4+?