You can do that now. It’s called Roth IRA. I’ve looked at it, but I do not trust them to keep their end of the bargain. They’ll change the rules later on and begin taxing withdrawals.
One of the old-time rules of accountants is to ALWAYS defer taxes TODAY if you can. You never know what rule changes may occur in the future.
http://en.wikipedia.org/wiki/Roth_IRA
The advantage to a Roth is that you can withdraw principle without penalty. That’s what I plan on doing if the Cyprus grumblings reach here. In retrospect, I wish I’d have taken my retirement cash and buried into the ground. The government can no longer be trusted not to confiscate private property.