I made a little drawing way back, of a sequential setup that I have never seen done before. It's floating around one of these threads somewhere.
Basically, you run a large turbo in the msp's stock location, and a smaller turbo where the stock airbox sits. Exhaust manifold feeds the large turbo just like a normal single turbo setup. Connect the turbine outlet on the large turbo to the turbine inlet on the small, with a pressure actuated exhaust cutout in between them.
Compressor outlet on the large turbo goes to a FMIC and then up toward the TB. Compressor outlet on the small turbo runs straight up towards the TB and is Y-piped with the larger. A pressure actuated solenoid flapper valve will open and close the smaller turbo's side of the Y-pipe.
Downpipe from the small turbo is tied into the exhaust system. Intake for both depends on where you want your MAF.
Fairly easy setup, the hard part is timing everything right. If you get your exhaust cutout in between the turbos and the flapper valve in the Y-pipe timed right, you have a perfect sequential setup. Small turbo spools and goes right into the motor, indirectly spooling the larger turbo. Once your large turbo is spooling, the Y-pipe closes, cutting off the feed from the small turbo (and preventing any backwards pressure from going down the small turbo's compressor outlet pipe). At the same time, the exhaust cutout opens, letting the large turbo breathe freely with no restriction.
The only variable that I can't figure out without actually testing it, is whether or not the large turbo will create too much parasitic drag being in-line first. The smaller turbo might not spool quickly if the large turbine is slowing down the flow too much.
However you do it, have fun and post lots of pics!