I like using the Rossum Control Forge with the Pro 2. It lets you design any 8 stage Envelope shape you want, exponential or linear. But that's just the tip-of-the-iceberg; you can do so much more with it, too (LFO's, random, sequences, triggers, etc.).
There's a bit of a learning curve (at least for me), since it does so much, but it plays very well with the Pro 2.