I think the only way the Govt is going to get its hands on his coins is to let him use some of those coins for his defense.. if not, those 5 percent of all coins will be forever lost.
This is an interesting riddle. He might have saved the coins in brainwallets, in (comparably) tiny amounts. Even if they come from traceable SR sources, it is rather impossible to show that DPR has the key to them. It is possible to construct a recursive brainwallet with any number of addresses, which unfolds after knowing a single passphrase. Or use several different passphrases.
Since the total amount of commissions is not known, it is always possible to save some coins for retirement.