[fab13n]

The way courts generally work, they need a proof you've done something wrong to condemn you. If there are a dozen friends who had the wiping rights to your keys, and they knew you'd been arrested, any of them could have decided to wipe the key, just in case.

Unless the judge can prove who did it, he can't condemn the 13 (12+you) of you because one of you did something wrong. Besides, the 12 innocents don't know who did it either, so they can't snitch.

It requires the wiping procedure to be impractically hard to trace back, but that can be done.

[anateus]

Unfortunately, setting up such a scheme is clearly intended specifically to create reasonable doubt, which can get you charged with obstruction and contempt.

[eru]

You can also require at least 2 or 3 (or so) of your friends to all press the key to wipe your data. That way you don't have to trust everybody completely.