Redmine

I've added a custom field to time registration in our setup, which contains an id for a "finalized time report" for a given project.

Once a month, a person goes into the report page and generates a report for the entire last month. When done, he ticks off the "finalized" field for all the time registrations that have been put into the report. Well, actually he enters the ID of the report, but whatever, that's not important.

There is currently a date/time filter on the report page. He would like to have a filter on this custom field as well, so he can do a search like:
Time/Date: Beginning of time --> last day of previous month
Report id: blank

This would give him all the time entries that he has not put into a report yet.

I'd like to put some time into making this happen the best way possible. I was thinking of a more general solution that makes it possible to filter on any of the custom fields defined for time entries?

What do you think?