Reporting Services security migration from native mode to sharepoint 2013 integrate mode

I already migrate the reporting services 2008 R2 native mode items, shcedules, etc. to my sharepoint 2013 reporting services, all works fine with the migration tool that microsoft has. But i have a problem. I need to migrate the security also. This is because my company has about 1500 reports with security in the native mode. How can i migrate the security to sharepoint 2013? or what else can i do to replicate the security?Thanks for any advice.PD: The microsoft reporting services migration tool is wonderful the only missing feature is security. !!