SA Dual Expression Pedal
I have one and it's great! Sure it's not cheap, but its kinda made for SA pedals, and it works awesome with others (I use mine with a Zoom G3 and EQD Rainbow Machine).
I have not used this with a BEF Pro, or any other SA pedal, but like I said, it was designed to work with them.
I've used an EP-2 and found the design lacking. The treadle was not smooth, and actually stuck often. Worth $35 I guess, until it doesn't work right.
The SA Dual-EP is tank-like.