I have to say that this is not permitted in my view due to the prohibition on BoJ. Furthermore as VN is a pretty well-known restriction code that forbids break of journey on the outward portion, and Virgin TMs know this trick people play with stopping short on tickets to north Wales coast destinations, I don't think it is worth risking your PRIV for it, on the odd chance that you run into someone who takes this seriously.
The way around it is instead of buying a London Terminals - Shotton Off-Peak Single, buy a return in the opposite direction, a Shotton - London Terminals Off-Peak Return, for a princely sum of 25p extra, throw away the outward portion, and break your return journey at Crewe legitimately.