Pitching Subscriptions to Google Referrals...W/out Getting Penalized?

The LA Times doesn't show Google referrals the articles Google indexed...

[sisyphus]

We are charging our users a subscription fee to allow them to search more than 30 days back in our content (which is mostly in message board form).

We're concerned about users working around this by searching us via Google (they index us daily). We could intercept all 3rd party referrals to content 30 days old or older, and tell them to subscribe to see the content. But I'm afraid we'd be penalized by Google.

BUT!

strangely, the LA Times manages to do exactly that. For an illustration, go here [google.com] and click the first link. You're not shown the article...you're given a subscription pitch.

Anyone know how they manage to do this without angering the Google Gods?

Any general thoughts (or pointers to resources) for sites in our situation? Obviously worried about Google Cache, as well (though the inability to click through entire threads in cache makes it less worrisome)

many thanks!