Bulking or supplementing?

Let’s say you have written hefty novella (as I have) and submitted it (as I did) to a publisher who wants novel-length works (as he did).  The story is complete with beginning, middle and ending.  The story arc is complete.  How do you make a 45,000 word thing an 80,000 word thing without repeating yourself?  Here’s my approach:

First, I make an Excel spread sheet listing every scene and its page number so I can go right to the insert points. 

Second, I look for the following:

• Lengthy exposition without dialog and I find ways to insert dialog.
• Inadequately described people or settings and I describe them.
• Cold descriptions and I insert emotion or internal dialog.

 Third and last, if all else fails, I invent new characters or situations.  This is the trickiest part since it can reveal itself as ‘padding’ unless the new situations are relevant to the story.  Otherwise, a reader could be led up a tributary and end up thinking, ‘What was that all about?’