wrote:
Recently I tried to depart from an non-tower airport that has no
instrument approach procedure, and hence no instrument departure. I
was told that I could not get a clearance on the ground, even with
VIFNO etc., and that I would have to depart VFR and pick my clearance
up while airborne.


100% wrong. An IFR clearance can be given from any place. You are
responsible for terrain and obstructions until reaching the altitude
given by the controller. If no altitude is given then the start of
controlled airspace.