Only two things stand in the way of President Obama's new bank tax: Warren Buffett and the Constitution. But even if it's enacted, BernsteinResearch has come up with four ways for banks to avoid about a third of the tax, saving billions over the next decade. Here they are:

Using Goldman Sachs and Morgan Stanley as examples, BernsteinResearch calculated the firms would each pay somewhere between $10 to $14.4 billion over the lifespan of the tax ($1 billion to $1.2 billion annually for 10 to 12 years). Analysts Brad Hintz, Luke Montgomery and Vincent Curotto predict that the banks will take four steps to save about 30 percent of the total:

1) Raise Short-term Funds Differently. The new 0.15 percent tax applies only to certain liabilities. Right now, banks raise short-term funds via loans and floating-rate notes in the commercial paper market, which are subject to the new tax. But banks may be able to shift instead to wholesale brokered deposits (deposits which are then sold to third parties) sold by their money market desks, paying a fee to the FDIC equal to roughly half of the fee imposed by the new tax. By making this switch, banks would avoid 3 to 4 percent of the new tax.

2) Reduce Repos. A repurchase agreement is a short-term cash loan in which the collateral is a financial security. A dealer sells an investor a government security for cash, and agrees to buy it back the following day. The difference between the buying and selling price is the interest cost -- but this spread probably isn't worth it when you factor in a 0.15 percent tax. The analysts argue that banks will be motivated to cut back on these repos, avoiding 10 to 11 percent of the new tax.

3) Pass It Onto The Hedge Funds. This one's simple. Banks lend money to hedge funds. Pass some of the cost of the tax onto hedge funds by charging higher rates on domestic margin loans. Save 3 to 4 percent. Banks keep some of their money tied up in liquidity cushions -- rainy-day reserves that they can quickly cash. If they reduce the size of these, the reports authors say 8 percent of the tax could be offset.

With the possible exception of the "stick it to the hedge funds" plan, all of these bank tax strategies could cause problems elsewhere in the economy. Numbers one and two could have negative consequences for the commercial paper market (which companies rely on to finance their daily activities) and the trading of government securities. Number four raises the scary proposition that a bank tax intended to discourage risk could actually spur banks to draw down their reserves.

"It's going [to] encourage people to reduce liquidity to reduce the fee. And that's not a very good thing to do in early phases of a fragile economic recovery," Bank of New York Mellon Corp.'s Chairman and Chief Executive Officer Robert P. Kelly said in an earnings call Wednesday morning. "If our competitors in Europe don't have to pay the fee and we're trying to raise deposits in Europe, it's very expensive and we are uncompetitive. Global playing field is extremely important in our industry."

4) Reduce Rainy-Day Reserves.