There's always the nuclear option: threaten to release the detainees if Congress doesn't provide funding for another solution.
There is no nuclear option. Veto is not an option.
What people don't seem to understand is that this isn't a failure of democracy to act: this is what the American people want. We don't care that Guantanamo is open and we'd rather see it stay open than give these people a chance at a fair trial.
We are a government by the people, of the people, and the people have spoken.
Alas.
The fundamental civil liberties protections of the Bill of Rights and Constitution apply to all “persons,” not just citizens. For example, every person in the United States has the right to due process and equal protection; to criminal proceedings that afford a right to counsel, a jury trial and freedom from double jeopardy; to freedom from cruel and unusual punishment; to freedom from unreasonable searches and seizures; and to freedom of speech, religion and association.
http://www.aclupa.org/issues/immigrantsrights/animmigrationg...
Now, the Supreme Court has decided that Congress has de facto legislative jurisdiction over Guantanamo (in an opinion comparing the historical treatment of Scotland, in which English habeas rights did not apply, to Ireland, in which they did): http://en.wikipedia.org/wiki/Boumediene_v._Bush.
Scalia's dissent was the most legally sensible: 'Justice Scalia added that the Court's majority "admits that it cannot determine whether the writ historically extended to aliens held abroad, and it concedes (necessarily) that Guantanamo Bay lies outside the sovereign territory of the United States."[27] Justice Scalia pointed out that Johnson v. Eisentrager (where the Supreme Court decided that U.S. courts had no jurisdiction over German war criminals held in a U.S.-administered German prison in China) "thus held—held beyond any doubt—that the Constitution does not ensure habeas for aliens held by the United States in areas over which our Government is not sovereign.'
But the Court stopped short of saying that foreigners in Guantanamo have the same habeas rights as U.S. citizens on U.S. soil, probably because of the strained nature of their conclusion that they had any habeas rights at all.
What it means now? Who knows.