There's something I'd like to point out, although Chris most likely already thought of this.
Given that the aliens have the tech to reach Earth, it is therefor possible for them to disguise themselves as us. However, that is not what I am going for, rather that they wouldn't NEED to disguise themselves as humans because other humans could do their dirty work for them behind the scenes of the political arena. Now, what I speaking of? I'm referring to human nature. We as humans are easily manipulated by others, if the aliens came and found a group of humans that were sympathetic toward them - and yes you WILL find them amongst society - then the invaders would make promises, deals, one's that they might ultimately break but enough to get the interest of these individuals to work for them and thus use them for their own means.
This kind of method is NOT inconceivable, as we've seen it throughout history over and over again; granted, not from an alien race or anything but from our own however still it is not something that can be tossed aside and stated to be 'impossible. There are other methods as well that could work to make humans side with the aliens, some of which would dive into the realm of mind control while others more threats and unhanded methods.
At the end of the day though, there are multiple ways that humans could be made to work with the aliens and nothing is impossible to consider. Especially once you take into account just how naive us humans can really be. Frankly, I look forward to seeing what Christ comes up with
And yes I know this thread is two months old, but it got my attention