Mmmmm — now I’m confused!
I thought that the fuel system operated on a continuous flow basis from the fuel pump through a NRV at the pump outlet in the feed line (to prevent fuel draining back to the tank via the feed line) to the fuel rail, at the end of which is the fuel pressure regulator (FPR) which maintains about 40 psi in the fuel rail and allows anything above that pressure to return to the tank via the return line. Surely a NRV in the return line would prevent that?
The usual problem is that the FPR fails at a much lower pressure and allows fuel to drain from the rail via the return line on engine shut-down OR the NRV in the pump outlet fails and allows the fuel in the rail to drain back to the tank via the feed line on engine shut-down so that there is insufficient ‘hold pressure’ in the fuel rail even after the initial ‘priming burst’ from the pump (when you first turn on the ignition) to allow the engine to start.
In either case, that problem can usually be overcome by employing the ‘key cycling’ trick - i.e switching the ignition ON_OFF_ON half a dozen times before engaging the starter to take advantage of multiple ‘priming bursts’ to get the fuel pressure in the rail up to the required 40 psi to allow the engine to fire.
Since in an earlier post Darren says he has tried that trick with no success, I suggest that the problem lies somewhere else.