I first this, as stinky will, I'm sure tell you that I kinda started this whole thing (spectator mode thread).
Whatever. If it gets added, I don't care who gets the credit.
As for how to store it, it stores if
for that game only. At the end of that game, there is an option to show the game log, which is an alphanumerical string. Incomprehensible to humans, yes, but there would be a Code -> English translator, so it can be read. The string could then be also used in a "Spectator Mode" type thing, which take the code, and plays the game back. The game could be stepped through card by card, turn by turn, player by player, or whatever.
EDIT: Oh yeah. Storage.
The string can be saved as text, in a Notepad file, for example.