This is not unlike my suggestion about making in-game events give you "reward codes" that could be then used on the second map's start to get specific rewards there.
Not too hard to compile, if we simply go by checking for several specific achievements and then adding some extra "confusion data" to make these codes non-shareable.
For example, giving each unique game run a (hidden) "start code ID" and making those codes CHECK their integrity to correlate to that ID.
In that way, unless you copy the entire game save (and you can add a code to prevent that as well, something that would also read even more data, like the save's Creation Date or whatever else changes after copy-pasting it), you won't be able to activate those bonus codes on another computer or even another game run.
Again, not too hard to implement with a basic keygen and a few input-output events to make this work.
This is also an alternative approach at Multi-Maps, or rather Multi-Plays, as in playing a [New Game+] based on your first game's success.
I still find it a VERY GOOD idea, seriously.