This is the main drawback of the Fuji GW and GSW series cameras (the second one being the noisy shutter/film counter mechanism). The only way to close the shutter in "T" mode exposure is to change the setting by rotating the shutter ring to another value or to wind the film. Neither method is easy to use. It is quite difficult to rotate the shutter ring without causing the camera to move, even on a sturdy tripod. And if you chose to wind the film, every light source in the frame will leave a bright streak on the image, because the film will be wound a little bit before the shutter closes. Many users resort to using a black hat to mask the lens at the end of the exposure time, before winding the film to close the shutter.
My conclusion: dispose of your GSW690II safely (by sending it to me 😀) and buy a nice G690 BL, which has a very quiet shutter with a normal "B" setting and an interchangeable lens.
Cheers!
Abbazz