Searching in value list using related records

[McG]

I have a field (called class) using a pop-up menu that is selected from a filed in another table and only uses related values from another table.

The related value shows a subject, e.g English. When the user clicks in class they only see the 10 or so records from the related table (which has 100 records) which are pertinent to English.

My problem is that the user is likely to want to do a search in the class field. if they do this, the pop-up shows no values defined.

I need to be able to do a find from the currently selected records rather than from the whole set with the contents of the subject field retained for the search.

Has to be possible....no?