Searchable Field Level Security

Is there anyway to apply Field Level Security so the field is not visible to the user, but is still searchable? I was hoping masking would achieve this but it looks like this is not the case

The only solutions I can think of is to use copy_to on the secured fields to an index-only group field, which is added to the FLS fields.

@robmartin There was a similar case link, it sounds like you might have a similar use case. Excluding fields from source might be what you are looking for.