NEX7 audio: Defeat AGC? Or merge separately recorded audio with NEX7 video?

Hi all,

I've had my NEX7 for almost a year, and one thing I've always wanted to try is recording video with good audio patched in via the Mic-in jack of the NEX7 -- from a Line, not a Mic.

I only just learned about the NEX7's AGC ("automatic gain control") which automatic adjusts the levels. So, at quiet times, you wind up with a loud hiss (because the NEX7 cranks the gain). And there's no way to turn off the NEX7's AGC.

So it seems I have three options:

1) Use the Line-out into the NEX7 Mic-in, and live with the AGC hiss.

2) Use some sort of AGC-defeat device that sits between my Line-out and the NEX7's Mic-in

3) Record the audio separately, and then merge it with video shot in the camera.

I'm guessing #3 is the best way to go, but I'm not quite sure how to go about it.

Let's say I press record on the NEX7, and then I start recording audio on the computer -- and then I stop both, and transfer the video file over to the computer.

What is a good, simple way to merge the video with the audio, such that they're in proper sync?

My audio app is Ableton Live -- can this merge happen within Live?

Thanks kindly for any advice -- I had always thought I could simply use the Mic-in, but AGC is a significant problem...