Hi,
Yes, perfectly possible and very easy actually.
You need to use the "Get Axis" action and reference "Mouse X" which is a default input ( Check the input settings to see the whole list and how they are each set up).
basically, you will get the delta movement, even when mouse seems clamped to the screen.
Then, if you want to keep an absolute position value, you simply need to add this mouseX to the mouse position you picked when you started this behavior ( it may be when the game starts and you constantly keep track of the mouse Absolute position, which will be totally different from the actual mouse on screen obviously, but that's fine for your need I guess).
Bye,
Jean