The only way I've seen a passcode "shared" was through the same system, using two different log-in names.
Each code that comes with the game is specific to the disc itself so once you use it, it's used for whatever system you put it on.
Same goes for the Premium code once you use that on a specific system.
All it does through this is create separate profiles on BF3, on the same system, with all the DLC included if you use the Premium code.
TL;DR - If you have the regular copy and the Premium copy, both will be able to play online, but only one will be able to use the Premium code because sharing it isn't possible.