Your original question was how to fold a map so the coordinates still show. I responded with printing several smaller maps. That the trail isn't on any map wasn't what you were asking.
So, three solutions:
1. the old fashion way....map, compass/pocket transit, altimeter, and plot the trail as you hike.
2. GPS and track log, print to a topo map via software.
3. Zoom in with Google Earth and see if the trail shows up in the satellite photos. Print, go hike. This is how I find little known off-map trails. You can do this with your iPhone.

What purpose would a map serve, you having already hiked the trail....don't know.