Hi Fabio
I was under the assumption that you had 2 distinct video tracks.
Here is what I think is the easiest way out for you short of re-recording.
1- Duplicate your video track, one on top of the other.
2- Split your top track in order to separate the 2 tracks.
See attached pick for what I have used. There are other ways to do this but this should work for you.

Cheers !
PC Win 7 64-bit 16gb Intel® Core™i7-2600k Quad Core 3.40GHz NVIDIA GEFORCE GTX 550 Ti
Cameras: Canon XF305 + Canon XH-A1
\’\’When the cutting stops, the editing begins…\’\’