Hadn't thought about this problem too much before as I haven't flown a two blade'er, apart from my one and only go in a Robbo.
However, may I suggest that this blade tie down on start problem could perhaps be prevented if a suitable reminder flag or placard was made up, to go inside the aircraft whenever the blade tie-down was used, perhaps hung on the controls or in the eye-line of the pilot over the engine instruments.
Whilst I worked on a police air support unit, we had a few scares with the inside transparencies misting up just as the aircraft was transitioned away on a no-notice callout. This is obviously extremely dangerous, especially at night. We subsequently obtained a compact ceramic element electric fan heater, which was left running in the aircraft when necessary to keep it warmed up inside. That completely alleviated the misting problem but there was a danger that the aircraft might get airborne with electric cable still attached. We made a large warning placard which was hung on the rotor brake to prevent that (allied with a suitable SOP to mandate that the placard was always placed first and removed last and mandated a clear responsibility for the pilot to check that the heater and cable had been removed).
Could this work in this instance?
One other thing that did occur to me about this. Placing the blades at 90 degrees to the aircraft should ensure that when the engine is started, there will be sufficient clearance between them and the adjacent aircraft - which would have prevented a ground accident that occurred in the north of England recently...