Years ago we had numerous aircraft types of various vintages and design concepts owned and maintained by the UK test pilot organisations. Other nations did likewise and with mutual cooperation across nations this gave an extensive list of aircraft for test pilots to fly inside the military domain.
Costs money though.
Much cheaper to contract to one company (who prefers collecting and storing documents, rather than reviewing them), who contracts another, who contracts yet another, who then hires an aircraft from an individual who operates on a PtF, complete with an installed engine that has never been overhauled in its 24 years of service. For safety, just add a PIC with little currency or experience on type, no supervision, questionable ability, a cavalier attitude to rules and regulations, doubtful airmanship and a madcap scheme to hand a forced landing to the front seat occupant (even if not qualified and on his first trip) as he doubted his own ability to execute one from the rear seat.
Seems a perfect mix to conduct extended envelope spinning, both erect or inverted and expanded envelope flying. Best not worry the aircraft & airworthiness owner though, the PIC can just send a quick email to state that it would just be gentle and benign flying.
I had known Alex for 20 years and flown with him in a number of aircraft types. He deserved better than this.