This is one the very few times that I do not share your view.
I gave some hints that the development of the negative has to be stopped:
"The idea behind it is to produce a negative, dissolve the remaining halide…
The Polaroid technique added to this all the feature of instant development
(fast, chemicals in pods etc., later even self-controlled with SX-70).
After processing and forming of a positive image behind the screen by those migrated and developed halides, the second film is torn off.
As there is no parting of the layers it must be self-controlled."
Further more this thread is clearly directed at people who have some practical understanding of the common instant processes.
However the aspect how to save the positive image from being harmed by the remaining halide solvent, developing agent and alkali is even merely paid attention to in the literature I used. With positive exception of the Neblette.
The only advise feasible for home projects I could give besides washing, is to use resin coated paper for the receptive layer and think of an acid water based lacquer similar to the one used in some Polaroid processes.