Another idea i found on a indie game on PC !

You press mouse button anywhere on screen, it becomes start position, form here if you move mouse to the right , the character moves to the right etc ...
if you release the mouse, the character finishes it's running by decelerating and stay in place doing nothing.
Depending on how far you move the mouse from the start position, the characters walk or run.
It's another similar but lot more intuitive way then having to really target the virtual joystick with the mouse, that will break a lot the fun and fluid gameplay of the game !!!

Just my personnal point of view !