IFileDialog customisation

[ajh32]

I'm using the IFileDialog with the CLSID_FileOpenDialog for an open file dialog. I've created an instance of IFileDialogCustomize so that I may customise the open file dialog slightly. I want to make the 'File name' control read-only, but I can't seem to find the control ID for the 'File name' combo box, or work out how I can set the control as read-only. Is anyone able to advise?