However, the reinstatement of the president’s power of impoundment, taken away by the Budget Control Act of 1974, would give the president much the same power as a line-item and would certainly be constitutional.
Impoundment was the power that the President had earlier to just not spend certain funds that Congress had allocated. This would serve as a brake on certain spending like the "bridge to nowhere" and other wasteful crap. The President would just set aside the money that would have gone to the bridge to nowhere and it would be sent back to the treasury.
An independent accounting board, modeled on the Federal Reserve (which keeps the power to print money out of the hands of Congress) would accomplish that. It should have the power to set the rules of accounting for the federal government, “score” the costs of new programs (which the Congressional Budget Office does now), and monitor all federal programs for cost-effectiveness (something Congress often forbids government agencies to do, obviously fearing what it might learn).This I think would be the reform we would need to fix the system. Take the spending out of the hands of the Congress and the White House and expand the powers of the CBO. Call it the Federal Spending Commission. The Congress and the White House would have to offer their budget to this agency who's sole job is to keep things cost-effective unless their recommendation is overturned with a 2/3s majority. Also give this group the power to audit the books of the Federal Reserve as well to maintain checks and balances.