"If you don't own the private keys to the wallet containing Bitcoins, you don't own Bitcoins."
Put your BTC in brain wallet. Tell IRS "I don't have the private keys to that address".
Impossible for them to legally prove you are the owner of those BTC.
You pay no taxes.
With brain wallet you risk brute force attack or with a suitably hard private key you risk forgetting it. Don't use brainwallets. An encrypted wallet with plausible deniability e.g. truecrypt is probably good enough.