Why not use the express slot to put in card that gives you two more ports? I had one that gave two USB 3 ports. To one port I connected my Lexar USB 3 dual slot reader (which does UDMA 7 for 1000x CF cards) and to the other port I connected an external HD. No need to constantly swap devices on a single native port.
Another choice is to go ahead and swap out the MBP to a newer version that has multiple USB 3 ports plus the native SD reader.