I give you one point for outside of the box thinking...+1
Unfortunately, though I hate to be the pessimist, I think this is a bad fit for this application.
First, for the purposes of this car, the extra weight would again hurt more than help.
Second, they're less efficient than using a single power adder (the reason you see huge power from compound setups (blower+turbo) is due to the cubic dollars invested in the projects. I seem to recall a recent, in the last year or so, magazine article where they tested a compound setup vs. turbos vs. superchargers. I know that the turbo combination made the most power. I don't remember if the blower combo made more power than the compound combo. The only merit I see to doing this is that you'd change the overall shape of the powerband. Like you said, you'd have the low-end grunt of a PD blower and also the added effect of turbo once it builds boost.
Third, extremely complicated engines require complicated tuning and uncomplicated racing. The nature of road racing: high-winding long-durations at full-throttle would be absolute torture for this motor.
Forth, you'd need a deep pocket-book to put something like this together. We're talking custom fabbing, an awesome stand-alone and a lot of tuning time, plus the cost of the power-adders.... ouch!
That said, even though you'd be all over the track (over-powered) and it would push like mad through the turns (under-balanced), it would be the talk of the track and people would come to have their pictures taken next to the crazy son-of-bitch that built and drove it!