There is a good meet spot near North of the Border that has a table, umbrella, chairs.  On weekdays, local businesses keep it busy, but on Sunday it is likely to be quiet. You take the next entrance AFTER the one to North of the Border into a parking lot near a small Fitness business.  You can acces the ride by a short ride up the sidewalk then drop into Penasquitos on the left to a small old adobe structure.   The only thing you miss is the first lovely hill singletrack near the start.  The proposed route takes you to Wagon Wheel Crossing which now has a decent suspension bridge to get you to the usual north trail system.

Just a thought !