Input Mode Game & UI, but keep turning with mouse?

Hello, I would like to know how to interact with 3D widgets in my level, by looking at them, but do so without enabling mouse cursor and keeping full FPS camera control (Same as in Doom 3). I know I need to enable UI input but doing so also enables mouse cursor and I lost control over my camera. Any tips on how to do this? Please help!

Shameless bump