BB wrote:

I'm not on the Rules Committee but it's arguable whether a T&B that's
disconnected from power (or the on-off switch) permits flight without
reference to the ground.

... If you convince the CD,

No CD in his right mind would argue against it. At least the CDs I've
happened to deal with tended to be quite reasonable persons. Most
usually their goal was to organize a pleasing event rather than to annoy
pilots. But this is Europe, maybe US CDs are different?