The ultimate irony of nihilism is that when you bring it to its natural conclusion it renders itself meaningless. Thus, talking about any and all values becomes moot (which of course includes nihilism).

Now, if you look at moral guides with which we are conditioned through culture, they are essentially (and surprisingly universally) based on five don'ts -- no killing, no stealing, no cheating, no lying, no coveting. The other half of these guides is quite culture dependent (but there still exists a common theme to them) and it deals with how to get to the knowledge of absolute.

It's understandable that before we know the latter, we twist ourselves into pretzels to rationalize the former. However, once we see that there are no intrinsic values, it becomes clear that all is just a matter of causality (hence karma and similar concepts). And since causality is neither good nor bad, it simply works impartially, you can view it as inherent rules of the game (though, yes, that's just a concept, too -- however, it does not invalidate causality as such).

Knowledge of absolute also reveals the uniform nature of existence and consciousness. In other words, there is no difference in value of human and a speck of dust and the same "I" is at the receiving end of all experiences. And pain, although neither good nor bad, still remains pain (though, its actual perception changes quite a bit).

So, to answer your questions, you avoid nihilism (or better said, transcend it, because at some point you encounter it so it cannot be avoided) by bringing it to its natural / logical conclusion. The "enlightened values" simply remain in the ballpark of the five don'ts, only now understood to be firmly based in causality and overall nature of reality.