i dont think u can cuz there are three wires in a 3 pin connecter on the white,green or some other colored one is the one that monitors RPM,s but when u switch 3 to 4 pin u can get the RPM because it will get connected to the PSu and not the motherboard which MBm 5 reads the RPM through
I don't have the WBK38 so I don't know what fan you have on it but for the RPM monitor to work a couple of things have to happen. First the fan has to have three wires coming off of it one of which is the signal wire for the RPM's. Second it has to plug into the motherboard not directly to the power supply. Third you have to make sure MBM is reading the correct location on the motherboard. If your fan connects to the power supply you will have to use fan bus that has a readout screen for the fans, something like the Digital Doc 5.