Your best mate is Shuttle Mate:
• 6 HP/TE width, 33 mm (1 1/3") in depth (super slim & therefore shuttle friendly)
• Merge MIDI and USB-MIDI into one MIDI and USB MIDI flow
• Perfect mate for Shuttle Control to be able to connect two MIDI devices into Shuttle’s 'to host' input (for example, drum 
machine or sequencer and midi controller).
• no bus-power required—device runs fully on power delivered from USB socket
• works also as a portable USB host for USB-MIDI only equipped controllers

• 6hp
• Module does not draw current
• 33 mm deep