What you're planning is an IFR flight on a combination of a Y and Z flight plan.
It's the exact same thing as a full-IR holder planning an IFR flight between two VFR-only airports. You depart VFR, pick up your IFR clearance en-route, climb into the airways and enjoy the glorious sunshine on top. Near your destination you descend, cancel IFR and continue VFR to your destination.
If your departure or destination airfield is below VMC minima, you can't make the flight, so you have to cancel or divert.
Obviously the transition from IFR to VFR is notoriously tricky since you and the controller need to work together to find a location where you can still be controlled as an IFR flight, but you need to be in VMC so you can cancel IFR. So you need to have VMC conditions above the MVA/MCA or whatever minimum the ATC controller needs to control you IAW IFR. And that minimum level may actually be well above what you'd require for a full-VFR flight.
That last bit may actually be the biggest catch. Suppose your destination airfield is widespread OVC015. It would be perfectly possible to fly to that destination VFR at 1000', but if the MVA/MCA level is 2000', you would not be able to achieve VMC conditions while under IFR, so you can't cancel IFR. And without a full IR, you cannot fly a STAR or instrument approach, either for cloudbreak purposes (using the ILS of a nearby field for instance, to get below 1500' and into VMC) or for a full stop landing.
Last edited by BackPacker; 2nd Jul 2014 at 09:40.