We actually added that exact feature last year in G5.5 (a free update for G5 users). At that same time we added other RC features like Aero Tow and Bungee launch, a timer gadget such as you might use on your radio at the field, improved wind/turbulence and thermals, and a simulated heli tail rotor flight failure.

To turn on the sky grid, from the main RealFlight menu select View->Effects and put a check mark next to Sky Grid. To change the look of the sky grid, simply edit the airport and modify the Sky Grid property. A number of different choices are available.

I hope this helps!