World nomads, which seems to use IHI BUPA, aka BUPA Denmark, as underwriters doesn't cover flying as crew:
World Nomads - Policy Wording: Certain underwriters at Lloyd's (AUS) effective 14 Feb 2013
But the brochure for travel insurance from BUPA Denmark itself does not specifically exclude flying as crew or passenger in non-commercial aircraft, so I shall investigate and report back here, but from what LeadSled says it sounds another option with QBE and Traffords:
Download travel insurance brochures ? Worldwide Travel Options