Need way to add field migration information to content/node types in migrate_d2d_ui

Drupal-to-Drupal migration UI does a good job of copying the basic fields of a node from Drupal 6 to Drupal 7, but I have 36 node types that are not basic Drupal content types, including ubercart products. I'd like a UI way to add the necessary field mappings and unmigrated fields to the complex content types, or to add the classes I've created that inherit from the Drupal6* migrate classes. Using the UI I can't specify the classes I've created to work with the default import of pictures, roles, users, taxonomies, files and basic drupal 6 content types which do work well.

(files do have one limitation listed in another issue about the source directory, but I have a workaround).