I did a lot of dirt rally and really needed a sequential but hated the Idea of having 2 shifters, or even worse settling on just H or sequential patterns for all games, so I came up with this basic design to allow for sequential shifting.

Assembly:

• Put 2x springs inside each tunnel of the adapter and use 2 5mm M3 screws on the side of the adapter to secure the springs. You can use a variety of springs for this as long as they are strong enough to return the system neutral, I'd bet orange bed screws might work well for this, though they might be too strong.
• Use 2x 20mm M3 screws on the top of the adapter to secure adapter into top plate. IF YOU AREN'T USING MY 6 SPEED PLATE, PLEASE USE ADAPTER AS GUIDE TO DRILL 2.5MM HOLES INTO CURRENT PLATE FOR MOUNTING.
• Unscrew Knob and slide adapter over shaft over the 3rd/4th gear and screw the 20mm M3 screws down to secure. Done!

I've included my pre-drilled 6 speed shifter plate if you'd rather use that.

Credit where it's due, BIG thanks to CET3D for making the OSS Shifter and specialfred453 for 6 speed plate I modified!