Originally Posted by kabuki-joe
just to inform anyone that may be searching for this as well, the reason it cant be done is a limitation of FAT32 which doesnt allow file permissions.
Couple of things...
1) Your /sdcard is not formatted in FAT32
2) The limitation is that Android is designed specifically to not allow you to change /sdcard permissions. /sdcard is mounted at boot with a specific set of permissions which are what the system wishes to maintain at all times, for all files.