Applying a fade/gain envelope to a distortion effect

[Matthew28641254c8g3]

I'm tring to apply a distortion effect to a clip and having it gradually increase in intensity by the end of the clip.  However, I cannot find an envelope SPECIFICALLY for the distortion effect, not the volume nor the pan envelope. 

[SteveG_AudioMasters_]

The only automation controls available for the distortion effect are these:

[Richard M Knight]

I would make two tracks one clean and one with maximum distortion, then do a crossfade between the two.