Hi Michael, probably your best bet for something like that would be the Construct > NSided command.

But you want to leave a somewhat larger and more regular shaped area for NSided to fill, not one with needle-sharp corners like what you currently have. So to prepare it, I cut those blend pieces in half lengthwise, by separating them out to be individual surfaces, then selecting them and running Edit > Trim and then pushing the "isocurve" button that is an option in Trim when you are working on a single surface. Then along one arc edge you can select the midpoint of the arc and that will cut the surface in half lengthwise. Then I picked the inner part as the piece to delete. There was also a teeny tiny face fragment hanging off the corner of one of those pieces which I deleted. I then also used the Merge command (http://moi3d.com/3.0/docs/moi_command_reference10.htm#merge) to merge the separate consecutive edges together into single edge pieces.

So with that preparation of basically widening the hole a bit, it looks like this:



Then that kind of boundary without very narrow sharp corners in it can be filled well with Construct > NSided, you can adjust the bulge factor in the command options down slightly to reduce the amount of inward dipping:


It looks like this shaded, seems to be pretty good (3DM model file also attached here):


Hope this helps, - Michael