Not if you think it through.
A parallel Justice System means competition for the honors and graft that flows to judges in the existing system. The last thing attorneys and judges want is competition that redirects part of the cash that sloshes though the system.
No, there could - by definition - never be a parallel system. There could only be a system that accommodates sharia to a greater extent - the attorneys and judges would still control it, to their profit.
Trust me attorneys and judges got way more than enough money flowing through