Create simple mission with aircraft at a Lat/Long of my choice

I have the basic map and the Syria map. I would like to start in the air at a Lat/Long (and altitude, heading) of my choice (of course within bounds of my chosen map). (Altitude and heading, less important at this stage. ) I will be flying F18 Hornet. From what I have experienced, I’m allowed only near selected airports... and this limits me. Any help in creating a mission with this parameter would be greatly appreciated.