Does the Subform record source have a primary key (ID) (I presume so). If so, create a normal form based on the same record source, then on the subform double click event:
Dim rs as Object
Docmd.OpenForm "YourFormName"
Set rs = Forms!YourFormName.Recordsource.clone
rs.findfirst "IDFieldName = " & me.IDFieldName
Forms!YourFormName.Bookmark = rs.Bookmark
Dave