You can adjust the ring on the steering column to change how the gears lash and interact. This can help to remove the dead zone but it can also make the car very nervous at speed if you go to far. It's a bit of trial and error. Adjust, drive/check and readjust as necessary. Dead easy to do with an 8mm ring spanner
Unfotunately it will always feel numb with little feedback. Only way around this is a hydraulic or electric/hydraulic setup. Well worth it though I think.
Also, if you want to track the car, perhaps join the Z4 Track Day and Race Car Group on Facebook. Tonnes of info in there from people who regularly track their cars.
https://www.facebook.com/groups/520863040768702