I started at Shining Minds Seminary against the NW range wall. Flew down to the lake and turned into King's Bridge Canyon. Then straight south to the last waterfall before you get the southern range wall waterfall. Here is a hint. The north is the hardest part. Use the roads to lead you to the mountain passes. Another approach is to follow the water ways. Both will help you keep the land falling off quicker than your glider. Once you make the northern lake the rest should be gravy.
Here is my video to prove it can be done. https://youtu.be/ru8jDq3TuGo
+ l3ushwacker
Finding the passes through the ridge lines is the key. It is mainly a northern Kyrat problem. Once you get down to the north lake it should be OK. I tried one before this one in NE Kyrat. It went almost as far. It made it to the Tea storage outpost on the river. Really surprise the heck out of me. So I tried this one and got farther. You might try somewhere up in far NE Kyrat around the last fort. I haven't investigated that area for glider launch points. Might be able to get a longer one.