You'll give it a pitch curve that has as much negative as positive. Say -10 to 10. You also setup the three position switch so that one position allows you to startup the heli safely and once spooled up you can switch to the next position that allows the engine to actually increase throttle when you apply negative pitch. So as you go inverted you lower the collective to hold your altitude.

more stuff here
http://www.littlerotors.com/setup/pitchsettings.asp