Another technique that can sometimes be used is to put a little tiny disc into the center of the hole:



Then the edge of the disc and the edge of the hole can be selected:



And then Blend will create a surface there, which can be joined in:



If you have a split-up edge like you do on one side, you have to use Edit/Trim (with Add Trim points option) on the disc's outer edge to split it up into the same number of pieces as the hole and then do the blends with a pair of edges at a time.

- Michael