mongodb find by comparing field values

Is it possible to express the following SQL query in mongodb:

SELECT * FROM table AS t WHERE t.field1 > t.filed2;

edit: To summarize:.

1. using a third field storing "field1 - field2" is almost perfect, but requires a little extra maintenance.
2. $where will load and eval in JavaScript and won't use any indexes. No good for large data.
3. map/reduce has the same problem and will go trough all records even if we need only one