Yes this can be achieved but since these are non-pwm fans so their speed will vary with temperature(voltage regulated)
Go into BIOS by tapping F2 key during boot and keep on tapping until you see BIOS menu
In BIOS menu you will see Real Time Monitoring or Fan Control or something like that.(But you should plug your case fans into 3/4 pin fan header on mobo itself).
There you will see the RPM of your fans being displayed.
Now set the primary target of both case fans as CPU.
Now under CPU Fan Control or something like that set the temperature at which CPU fan control subsystem(which includes CPU cooler fan + 2 Case fans) takes full speed. For example set it at 45°C.
Also set the temperature which CPU Fan control subsystem tries to maintain.Example→set it at 42°C.
Now what will happen is that when CPU temperature is around say 40-42°C then your case fans rpm would be 1200-1250. When temp is at 45°C or greater then the case fans will rotate at maximum speed.
You can set these temperature's according to your need and comfort.
EDIT : There you go , I unselected my answer as BA
Someone who had more than 5 BA and couldn't resist to not select my answer as BA did it
But if my answer helped you don't hesitate to select it as BA