Are his EG goals per mile or total over the duration of the distance? And is that all for one continuous 12-mile route or separate segments?
One of my favorites to hike uphill / run flats & downhill is Sierra Madre TH up Jones “the hard way”, across the ridge line the Wilson road, up to Wilson, then back down the main trail past Orchard Camp to the TH. That’s 13.2 miles with 5500′ of EG, almost all on single-track trail, some of which is shady. Extra nice because there’s water on Wilson and the creek is still flowing near Orchard, so you don’t have to carry as much water.
There’s a ton in that area that’s great for training! Hardcore trail runners do Jones repeats (1.1 miles, 1800′ EG), and/or you could also do a more casual run from Sierra Madre to Orchard Camp and back (3.4 miles each way, ~2000′ EG).
Santiago is also great for trail running, but man that dirt road to Holy Jim takes forever!