I looked upon all of XDA trying to reach a solution to be able to run non-kexec roms alongside JB Leak 3 running in system 1 .
However after a lot of searching and scratching around managed figure out a way to get non-kexec roms working alongside JB leak 3
1) Backup the Kernel on JB Leak 3 on system 1 (Assuming you have JB Leak installed on system 1)
2) Flash boot.img of ICS (ICS kernel) on the JB Leak 3 . Go back switch system to system 3
3) Install Any non-kexec rom and corresponding Gapps in system 3 (ex : RAvi's PAC rom from 17th July 2013 , LS 2.9 by @Aceofzeroz)
P.S : Non-kexec ROMS have excellent battery Life
4) Reboot and click on the DROID logo at the boot and enter system 3....Voila u are booting Non-kexec roms sucessfully
Please Note : You cannot boot into JB Leak present on system 1 now..because you soft bricked it when you flashed ICS kerenl over it.....However there is no reason to panic.... If you want to boot into System 1 (JB Leak) , then Go to recovery and flash its kernel back , remember you had backed up in Step 1 to system 1. Then re-boot , you should be able to boot JB Leak.
HAppy flashing..... and enjoy the battery LIFE