I'd kinda be worried about the heat generated by the disks mounted directly into plastic... Depends on the type of plastic as to wether it will melt or not though..
Much easier option may be replacement rear steel wheels with disk hubs? Dunno about how well that would work mind.
I'll be going solid axle on my c5 variant, with a heffing (compared to yours) hydraulic motocrosser front brake mounted on the axle. Might end up going MTB hydro front brake too, not entirely sure yet!
But will probably need it with the amount of power it's getting.