Multi Camera Canon C100 sync solution?

[aestartia]

I have 1 canon c100 mark I . the first version not the Mark II. I need an easy go to solution besides a clapper board to sync up the audio and video. I am aware of the Free Run setting and 
the time code setting to get both the cameras to have the same time while shooting but it is still also of prep and setting to get that to work. There has to be an easier way to lock in the  
audio and video from 2 CV's . if it is a cinema line EOS camera there should be a simple way of doing it with a 100% fail proof method to make sure the 24,29 or 23 Fps MXF,AVI and so forth can sync 
up.  
 
I would like to know if there is a trick to this without having to spend money on an ATOMAS NINJA or pro res external recorder and even that I don't think can do what I need. I am aware 
of plural eyes plugin for various video editing software but i would like to have it all synced up so no work is needed in post in order to keep 2 camera multi shoot interview in audio video sync all  
the way to the very end . Also is there a very precise method more so than a clapper board to sync up the audio and video in a multi camera shoot with the CANON C100 mark I? because even with a clapper board 
 
 
you have to pay close attention to the video clips in post  cause they can get out of sync by seconds i am hearing. Please someone does anybody have a solution? I realize a canon  
c300 or above will allow me an easy precise automated audio video sync however I am wondering only about having another Canon C100 along  the 1 Single  Canon C100 Mark, I currently own 
 
Any advice would be somewhat of a relief.