It does require some expense and effort to invest 401k and IRA money in bitcoins, but I think "next to impossible" is an overstatement.

There are companies (like http://www.broadfinancial.com/self-directed-ira) that for about $1500 will help you set up a self-directed IRA and an IRA LLC investment company.  You manage the IRA LLC and have a wide range of investment options.  They are commonly used for holding real estate in IRAs, but bitcoins are 100% legal, as well.

If you do this with a Roth IRA, as long as you follow the rules and don't withdraw until age 59 1/2, you will never have to pay any taxes on the gains!  So if you transfer or rollover $10,000 to a Roth IRA LLC, and bitcoin goes up by a factor of 1000, you wind up with $1 million completely tax free!

I think it's worth a small investment of time and money up front to avoid paying capital gains taxes on the potentially huge gains bitcoin may bring us!

See https://bitcointalk.org/index.php?topic=396783.0 for details.