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It's hard to see how a President Obama (or whoever) voluntarily relinquishing some of the previously claimed executive powers would necessarily set the path for future executives.
Future presidents would still be unconstrained -- still able to pick up those previously claimed powers.
The only way for a parliamentary democracy to limit executive power is for the parliament to (re-)claim its own prerogative. Of course, we never quite adopted parliamentary democracy here. Maybe that's a problem.