I Learned from the Kenny Videos, specifically #23 under the Reaper 5 Explained column.
here
It seems there will always be some type of combination click involved at a basic level.. there might be some advanced feature that will do what you are looking for?
There are a few other Vids under some other sections that cover more advanced envelope work too.
I was able to fly through some envelope work last night and didn't feel as encumbered as I did in the past... That pen/writing tool is great. But for precise single points I think it's Shift+click..
YMMV
Happy Reaping