I've got from months a very useful tool kindly shared by the video game editor company, Epic Games !
The tool is called Carapace, you can build your persp grid so quickly, that's incredible ! Since it isn't the most intuitive tool to use, I'd recommend to watch the small introduction on youtube. However, it's very simple and effective once you know your shortcuts.
Hope it can help anyone who could use a lot some persp grid (which is very very important for landscapes )
Here is the link : epicgames.com/community/2012/1…