Hello Steve,
[Briefly, since editing full-format ODF files isn't officially supported]:
There's no way within an ODF to access the current or cued stepper frame numbers directly as 3-digit numbers. However, in Hauptwerk v6+ you could conceivably embed non-displayed switches (via Switch.DefaultInputOutputSwitchAsgnCode) for the appropriate functions which have illuminated buttons on the 'Combination stepper (all)' large control panel (e.g. the buttons for the cud frame digits, and/or the xNN buttons for the current frame). You could then potentially combine/encode the resulting states of those switches to CC values (via CC-linkages, etc.) to show them as numerical digits within your ODF. I don't think you could display the 100s digit of the current frame that way, though. It would be fiddly, and I'll have to leave that one to you if you want to try it.