How to add a extrude cut to a sheet metal rolled pipe in the flattend state ie no bends so cant fold/un-fold

I have a fabricated rolled pipe with a seam join that I have created as a sheet metal base flange. I wish to have a slot cut in one side of the pipe that can be laser cut in the flat pattern. Because the rolled pipe has no bends as such I cannot use the fold/unlfold feature to add the slot in the flattened state. I have added the slot in the folded (rolled) state and then when I produce a flat pattern in the drawing the extrude cut profile is distorted

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