Brilling

Basically I am trying to find a way to set my expression pedal as a volume pedal so I can do swells. I want it to have the same function as the auto volume echo, but I want to be able to control the swell, when it comes in, etc... So far I have been looking through manuals and googling and not found anything on exactly how to do that. Is anyone able to point me in the right direction or explain in detail how that would be possible to do? Thanks!