Your avatar is amazing, holy wow.
Ok ok, anyway.
I did a collab a few weeks ago and I was scouring online for basically what you are asking now and some people suggesting doing a google hangout and recording it? But I personally, was having issues because google was being silly that day and kept dropping our call.
We ended up doing a skype call and recording each other on the screen (I have a mac and just whipped up Quicktime Player and did "video recording") then I had him send over his video then put it side-by-side in iMovie and matched up the audio with the visuals.
Honestly though, I'm just gonna keep an eye on this thread because I would love to see other peeps' response for a better way to do this...
Good luck, Ciarra