It's been 6 months and our client is still asking for this.
You mentioned you logged the feature request. Is there any update? Is this on the radar or far down the list of things you might do soon?
If not, it looks like I might have to proceed with custom filtering. Is this still the preferred approach? I cannot simply create a custom filter expression, but I must customize the entire filter control and replicate the existing filter expressions and then add my new one?