I fantasize about doing this daily.
You also might consider a 401k loan. That way if your bet pays off, you don't forever lose the tax sheltered status of those dollars.
Edit, on loan limits:
The maximum amount that the plan can permit as a loan is (1) the greater of $10,000 or 50% of your vested account balance, or (2) $50,000, whichever is less. For example, if a participant has an account balance of $40,000, the maximum amount that he or she can borrow from the account is $20,000.