Although it's standard operating procedure to add clauses to unrelated bills for funding purposes, they are certainly more subtle than 1.5 billion dollars to a hidden account. I mean - it wouldn't even be hidden if it were part of a bill.
Also, the President can not give the go ahead for the NSA to wiretap US citizens. The NSA's charter specifically states that they have no business spying on US citizens in domestic affairs.
Furthermore, this scale of wiretapping could very well have to be authorized by the Supreme Court due to the right to privacy enumerated from the Bill of Rights (and upheld by the Supreme Court) and the fourth amendment (illegal search and seizure).