Wireless DC Motor Speed Control
Here's a first pass:


Check out sites like Pololu for DC motor controllers.
These can be easily connected to Arduino, and libraries and demo code are readily available.


ie: no need to run a servo to turn the knob of that "recommended" motor controller.


Various wireless solutions for Arduino are available, again with libraries and demo code.


It's a pretty easy path to gluing this together, so long as you have at least some programming background.



As an alternative, there are DC motor control accessories to connect up to R/C (radio control) gear, like these:

http://www.robotshop.com/en/rc-motor-controllers.html

... which might be more turn-key at some cost in getting it to do exactly what you want.  It seems like you are in the neighborhood of robot remote control, so that's probably the place to sniff around.

-- Graham