Best way to hold mouse cursor on control while activated?

I'm fairly new to unity, but picking it up pretty quickly and have a decent application going. My application is not a game, but you could think of it as having similar mechanics to a point and click game.

On the screen are various controls drawn on a background texture, and in front of each control I have a planar object with the renderer disabled that detects mouse events on the control.

The controls include a joystick and some rotary controls, and on these controls, I click and drag to change the value. For example, I click on a rotary control and drag it upwards to increase the value, or downwards to decrease.

I found it annoying that the cursor would move around while I'm using the control, so I added this bit of code (C#) to my OnGUI() function:

 Event e = Event.current;
             if( isMouseHold ){
                 cursor_curr = mouseHold;
             }else{
                 cursor_curr = new Rect( e.mousePosition.x-cursor.x,
                                         e.mousePosition.y-cursor.y,
                                         cursor.width,cursor.height );
                 mouseHold = cursor_curr;
             }
             GUI.DrawTexture ( cursor_curr, cursor_main );

The problem with this is that Event.current.mousePosition continues to change, and only the position I'm drawing the cursor is held, so when I stop using the control (i.e. set isMouseHold = false) the cursor jumps to the current mouse position.

I assumed there would be a setMousePosition() function/method somewhere, but all information I can find says there is no such functionality in unity. Screen.lockCursor doesn't seem to be of any use for this kind of scenario either. So, I'm wondering what the common practice is for doing this sort of thing. Point and click is a pretty popular genre in indie game development, so I'm thinking people must have a standard way of doing this.

tl;dr: What is the best way to hold the mouse cursor while a control is being used without it jumping to the new mouse position when it is released?