Squish on Trimmed V Valid surface

Hello Chaps,

Sorry if the whole squish v Smash v Unroll for boat hulls is getting boring on technically non developable surfaces but I use a production method that should negate the problem or at least it does using traditional methods. I just need to replicate it with Rhino.
Basically I need to generate flat patterns from slightly curved 3d shapes that retain the edge geometry. Im working with Aluminium sheet of 2mm or 0.080" and I can introduce as much 3d shape within that boundary as I like by using an English wheel without significantly affecting the outer boundary geometry. To help anybody not familiar with an English wheel, it does that by squeezing the sheet thickness over the middle area of the sheet between two steel rollers. That thickness is reduced and the material is dispersed into extra length and breadth of the sheet there by introducing 3d shape.
It seems like Squish should produce what I need as it has extra parameters to tune the stretch and compression but even using the preserve boundary option it does not and the surface edge dimensions are not preserved.

Using Smash I get better preservation of edge length and curve shape but I get two very different shapes all parameters equal depending on whether I apply it to a surface described as a Valid surface or described as a Trimmed surface. Smashing a Trimmed surface retains good boundary curve shape but a surface that is described as a Valid surface looses one of its edge curves which is replaced with straight line.
I don’t even know how I generated a Trimmed surface Ive been playing with it for a while and now can only generate Valid surfaces. Im using Sweep 2 rails to generate my surfaces.
So my question is can I convert a valid surface that was generated by sweep 2 rails to a trimmed surface so I can apply smash or am I following the wrong path, is there a better technique that better suits my production. All I need is to preserve edge shape and edge length when its flattened, the middle of the sheet is irrelevant as I can introduce all the shape I need to the sheet later.

Hello - long shot in the dark but DupBorder, then ExtendSrf on the non-trimmed ones to get them out past the edges, then trim with the original border curves.