MIDI Yoke is normally used to connect two applications together. The first application will open MIDI Yoke 1 as an output port, and the 2nd application will open MIDI Yoke 1 as an input port. MIDI data will travel from the 1st applications output to the 2nd's input.
Single Client to Multi-Client: You can use MIDI-OX in conjunction with MIDI Yoke to achieve a virtual multi-client input. Launch an instance of MIDI-OX. In MIDI Devices... dialog, select the single client hardware driver as input and select MIDI Yoke 1 as output.