Can I add data fields to Insight Reports

Content

I know Insight Reports only returns a small set of data fields in the initial view when a report is run and that I can add additional columns/data fields from a predefined list of available fields.

Is it possible and what is the protocol (Product Improvement Idea? Service Request?) to add specific data fields that are not in the predefined list?

For example, if I want to build a report for tracking an assignment I do have available to me in the LearnCenter Report "ItemCompletionDate", but that does not appear to me to be available when I run an assignment report in Insight Reporting. I'd like at least to be able to add some of the fields that are standard in the database, and even better would be to add some of the custom fields established in our original system implementation.