You cannot install apps onto ISE.
You can setup an external repository to handle scheduled backups
On-Demand and Scheduled Backups
Cisco ISE provides on-demand backups of the PAN and the primary monitoring node. Perform an on-demand backup when you want to backup data immediately.
Cisco ISE also allows you to schedule system-level backups that can be scheduled to run once, daily, weekly, or monthly. Because backup operations can be lengthy, you can schedule them so they are not a disruption. You can schedule a backup from the Cisco ISE Admin portal.
http://www.cisco.com/c/en/us/td/docs/security/ise/2-2/admin_guide/b_ise_admin_guide_22/b_ise_admin_guide_22_chapter_01011.html
