[pct-l] Really Mexico to Canada

[mark v]

I asked this Q over at trailforums once but didn't really get an answer, so i'm going to try here.

We all probably know that the PCT doesn't start in Mexico.  Even if you stick your foot under the border fence, the problem is both sides of that fence are still USA soil.  You have to go some further distance before it's actually Mexico.  (What is that distance?  50 yards?  A quarter mile???)

So, i'm wondering if anyone has started their hike IN Mexico, how they did it, or if nobody has done it, how might you try?  

In looking at a road atlas, it seems the closest legal/normal checkpoint is about a half-days walk to the west of Campo.  One could get dropped off, walk up to the checkpoint, explain what you're doing (show your passport) and that you'll be walking back in moment, and then just roadwalk to Campo.  I'm wondering if this would create a problem, or if there is a better way.  

I thru'd in 08, and sometime when i'm back like for Kickoff or whatever, i'd like to connect those steps so i can feel like i've gone all the way from Mexico.  Thanks!