Someone has already thought about this...
Excerpted from the RAPTORHELI-list
Hey everybody, 
Nobody wants to crash..., and it's something you might not want to think about, but I have seen how the FUNKY CHICKEN can ruin a motor.... Luckily, I haven't gone through the experience of having to stand there, and watch my heli flop around until finally burning up the clutch bell lining, and ultimately, a motor.., and I am hoping that I never have to.
I don't know why it took me this long to share this idea with you guys, because it is something I have been doing for a long time now.
I have been placing a light spring between the servo arm, and the throttle arm, so that if the throttle linkage pops off in a crash..., hopefully, the throttle will be closed instantly. This only works out that easily if the throttle barrel closes when the servo arm pulls. If not, the spring might have to attach to something else. On my OS 61 SX wc, I just use the other side of the throttle arm to attach the spring. I attached the spring from the furthest hole in on the servo arm, and to the furthest hole in on the throttle arm..., so as to place a lighter load on the throttle servo. This has likely prevented the funky chicken at least once for me, if not more.
I am lucky enough to have a really good local hardware store nearby that has just about everything you can think of in stock (McFaddendale's, in Las Vegas). They have an impressive array of springs in stock. I noticed the display for the springs one day while I was in there looking around for other stuff. I don't even remember if I had come up with the idea before I bought the springs that I use, but I selected light duty springs that range from about 1 to 2 inches long. The coils are about 3/16 diameter. The spring wire is very light gauge, and so it is light in weight, and doesn't pull too hard.
I haven't had any RF problems that I know of, but I run PCM receivers. I am not sure if the spring might cause interference by rubbing against the metal throttle pushrod, but I guess you could use shrink wrap on the throttle pushrod if you are concerned about that issue..., especially if you are running FM receivers.