if it can be done what would be the benefit? memory speed? not worth the crash. I use highspeed u1 micro sd cards which work fine. u3 good too. extroot copies all files so no need to manage internal memory. benefits of using 1 location far exceed the headaches. also you can do backups really easliy and revert back with a file copy.
so after creating extroot on micro sdcard or usb drive. you have 3 directories.
upper
etc
work
if you copy upper you can always copy it back so you can do a full backup of the os and then revert back
etc holds the info of what is going to be mounted at boot instead of internal memory.
work is I have no idea but it needs it.