Brushless motor controlled via current source math model
If you are driving the motor with a known voltage, the page you linked to gives you the answer so I assume you want to drive the motor with a controlled current.

Since the motor's torque is proportional to current, you can forget the resistance, inductance and back-emf constants.

\$T = K.i\$

and

\$T=J\ddot{\theta}+b\dot{\theta}\$

this can be expressed as 

\$s(Js+b)\theta=Ki\$

(from your linked article), so

\$\theta = \dfrac{Ki}{s(Js+b)}\$

and

\$\dfrac{\dot{\theta}}{i} = \dfrac{K}{Js+b}\$

Of course any current source has a finite voltage compliance, so you will also need to compute the voltage as a function of current to ensure that the current source stays under control.