You need to edit the Build.prop in root/system and add these lines:
# Storage configuration
persist.sys.vold.switchablepair=sdcard0,sdcard1
# Change to 1 for swapping SD cards
persist.sys.vold.switchexternal=1
It may not work on KitKat 4.4.3 or lower.so you should flash 4.4.4 CM11 or equivalent.
CM 9, CM 10, cm 10.1 and CM 10.2 will all work.
Thanks anywaySimilar threads
