The K4/M4 mix is not actually a figure, but a morph of the combined figures created from the script. You would need an actual base to work from (either M4 or K4), which is why the clothes are getting destroyed.

Could you export that mixed shape created from the fitting room as an obj and use it as a morph target, similarly to a shape fit for an outfit? Then you could set the K4/M4 figure into the percentage you wanted then dial in the shape. You would have to do this for each variation you want to use though.