@TheComet
Or perhaps, since the grass objects are limbs, then you could load or create an additional copies as separate objects. Scale the original grass plane limbs to something ridiculously small, say, .0001,.0001,.0001 or even 0,0,0 if it is allowed without crashing. Using Limb Position x() y and z, position the loaded copy at the scaled down limb's position. Make sure the copy doesn't have collision detection set. You'd have to set the rotation/orientation to the original limb. When you update the main object using the collision commands, there should be a big gap in the triangle soup where you have shrunken the original limb. The chance of scoring a collision hit with the tiny limb is extremely low.
I would've suggested glue object to limb, but the object may inherit the properties of the original limb, in which case you'd have to scale the object up so it is the correct size.
Or, this comes to mind as I am typing, build 2 models, one with the limbs and one without. Setup the one without in sparkys. Then delete it. Now when you are checking for collision, use the deleted object number in sparkys for the collision detection NOT THE ONE WITH THE LIMBS but show the complete model. This should work if the full model doesn't change.
Enjoy your day.