I figured out a solution to my issue.
When the dataEvents type: 'change' occurs on the first select cell, I make my ajax call to the server, and the values for the other select cell are returned.
At that point I save that information using the jQuery.data() call.
Then, when the secondary cell is selected, within the afterEditCell event, the element exists, and I can replace the contents of the select with the data I saved earlier.
If anyone wants to see code, I can post snippets.