The single key shortcuts for the tools in Play mode do still work, but they’re not accessible when you’re using the Key Editor in Write mode because they conflict with note input shortcuts. See this post:
The problem you’re having with CC editing is that you cannot have two points at precisely the same rhythmic position. Dorico doesn’t (at the moment, anyway) provide a line tool with multiple nodes, and a particular point cannot therefore be both the end of one line and the start of another. The grid resolution for the controller lanes is very fine-grained, so I would hope that if you started your next ramp from the very next grid position after the end of the previous one, there would be no (or next to no) audible difference.