Hi Lars, probably your best bet for this is to use the "Patch" command in Rhino - it will kind of fit a single squishy surface through the curves that you pick.

It is not exactly the same as a true "minimal energy" surface like a soap bubble but it will probably get you the closest.

MoI does not have this particular tool yet, it probably will not be coming directly in MoI until MoI version 3.0 .

- Michael