If Awlaki is a turd-bag treasonous Islamo-fundi plotting to kill Americans on a foreign battlefield... whack him. That's fine.
That's the part I don't get; why can't we alter due process to allow for a trial-in-absentia, provided the accused is given adequate notice, (several months would have been insignificant in this case, since they could have given the notice a long time ago) opportunity for safe, paid travel to the court with promise of same to get home if acquitted, etc.? Surely we have the Constitutionally required two witnesses to testify that he's been at least giving aid and comfort to our enemies. Get a verdict and death sentence, and then carry it out through whatever means necessary.
Heck, get the sentence, then issue a Letter of Marque for a tenth of what the mission would cost, and watch the hunting guide and security companies team up to make a killing off the killing. How many people would pay $50k+ to legally hunt humans, much less terrorists?