Would it be possible for you to upload a few seconds of the bad video to the internet, and post a link here? If we can see the problem, we may be able to help come up with a solution.
If your camera was stationary, and your talking head wasn't moving much, a garbage matte and a new background, possibly a still frame from your interview, would probably do the trick. The biggest potential issue is that the flicker might be hitting your subject, which would make this look very unnatural, but I can't tell, since I can't see the video.
Worst case scenario, you can use your software to lower the contrast. This might solve some of your flicker problem, but at the expense of a greatly washed out, dull image.
Again, seeing a clip would help others to develop a solution.
If you can't get that to work, I'm experienced in After Effects and other special effect programs, and I can probably solve your problem. I can't do it for nothing, but I'm probably significantly less expensive than a round trip flight from the US back to Japan to re-film!