I think there's a big difference between flying under IFR and inadvertent entry into IMC conditions.
If you were flying VFR and suddenly encounter IMC conditions at Inverloch, you should rightly be feeling stupid to tell Centre you're switching to IFR - that just smacks of bad planning. You should contact Centre and get them to help you. You really should have been having an out behind you all the time. Worse comes to worst, a one-minute level rate one turn, preferably seawards (I experienced that once during my PPL days).
IFR flights require meticulous pre-flight planning over specific routes. Sure you can ask Centre to vector you all the way to Merimubula, but I find that somewhat irresponsible, handing the plate over to ATC and throwing away your map altogether, not to mention your responsibility to your passengers.
It's all about airmanship, really.