To disable thumb controls: "Clear Input Zones"

In mobile/defaultGame.ini have a look in the zone definitions for the joysticks, you'll see they point to a standard inputkey types ... have a look for them in mobileInput.ini . You'll see the code they run in PlayerInput.uc

[UberStickMoveZone MobileInputZone]
InputKey=MOBILE_AForward
HorizontalInputKey=MOBILE_AStrafe
Type=ZoneType_Joystick

[UberStickLookZone MobileInputZone]
InputKey=MOBILE_ALookUp
HorizontalInputKey=MOBILE_ATurn
Type=ZoneType_Joystick

input.ini
Bindings=(Name="MOBILE_ATurn",Command="Axis aTurn DeadZone=0.05")
Bindings=(Name="MOBILE_ALookup",Command="Axis aLookup Speed=-1 DeadZone=0.05")
Bindings=(Name="MOBILE_AStrafe",Command="Axis aStrafe DeadZone=0.15")
Bindings=(Name="MOBILE_AForward",Command="Axis aBaseY DeadZone=0.15")

PlayerInput.uc
.....
var input float aTurn;
...


You can either create your own input handlers or just use the existing ones