How to create ramp and max speed ?

I would like to use a pwm motor driver board and a potentiometer joystick to control the speed and direction of a 12 volt dc motor.
However, I need to have the ability to adjust the top speed limit and also to have adjustable speed ramping (acell/decel rate). The input signal that the board requires is 0v/2.5v/5v with 2.5 being stopped.
I have a circuit that creates these functions for an anaolg motor driver which requires a signal of -5v/0v/+5v. This circuit uses a pot fed with the +5/-5v to create the speed signal, and another pot and capacitor to create adjustable ramping of that signal.
How can I achieve this with the 0/2.5/5v signal?

Thanks,
Paul.

connect the -5 lead to ground instead

So it is possible? Thats good news. I tried using my original circuit as sugested, along with a trying few different caps and pots, but it is just not the same. Im not shure how to properly build this circuit.

Thanks,
Paul