Just so I understand your question, when you say "automatic" do you mean, how do you get it to start at one end and have it appear to grow to the other end, even if the curve is animated?
If that is the case, then my instructions above should work for that.
Key the max clip at the start of your shot at 0.
Then, go to the frame where you want to see the whole vine, and key the max clip at 1.
Then, regardless of the curves' animation, the vine should follow the path and reveal itself more and more each frame till its' max clip reaches 1
Now keep in mind that when your curve is animated, a PFX brush can be set to display on the curve based on the curves' normal direction, etc.
So be carefull there, as the brush will alter shape per frame based on those settings.
This means as the curve turns direction, the normal value can change to be a negative value, thus flipping the brush around in undesirable ways.
NOTE: attached is a sample Maya 8.5 file of an example test I made for you
Israel "Izzy" Long
Motion and Title Design for Broadcast-Film-DS