'Valid consent' provided by advance statement?

Continuing the discussion from If coercion is a necessary element of 'confinement' when could there ever be 'valid consent'?:

Another interesting question is whether it leaves open the option for advance consent to confinement (through some form advance statement not ADRT), where a person is able, and perhaps with previous experience of confinement, can state their ‘wishes and feelings’ are that - they are ‘happy’ to be confined in certain prescribed situations. Meaning that if they are ‘confined’ their advance statement would indicate that there is ‘valid consent’, as long as it remains within the prescribed circumstances (NB: this idea was raised with me by someone else, so isn’t my specific reflection but wanted to share to add to the discussion - they articulated the point far better than i have so apologies if they read this and I haven’t done their point justice).