OK, here's a first stab at it - slightly short of the intended 79 miles, which is easily remedied by continuing north past Tustin on lap 1... I think if we go up to Yorba park and turn around that'll do it.

http://ridewithgps.com/routes/1880338

I'm tempted to ride there, which would be an extra 20 miles (each way) but I have a feeling that's squarely in "bite more than I can chew" territory. We'll see. I haven't made my wife drive to pick me up in years... so there's always that option.