How to views-filter attached field value by calculated values?
I solved my current problem in a similar way to the solution here: http://drupal.org/node/1259914


Added a filter to the view with my taxonomy field as "not empty"
Implemented hook_views_query_alter() to call $query->add_where with my field_table_name.field_data_column and the values I wanted to accept with the 'IN' operator.


That said, I'm still interested in the views_handler_filter->query() solution(s).