Defining XLApp as 2007 App on a machine with 2003 and 2007 loaded

We've just deployed Office 2007 enterprise wide and I've just discovered that
some users still have Office 2003 on their machines because an application
they use hasn't been upgraded to Office 2007. Anyway, I have the following
snippet of code

On Error Resume Next
Set XLApp = GetObject(, "Excel.Application")
On Error GoTo 0

If XLApp Is Nothing Then
Set XLApp = CreateObject("Excel.application")
End If

where XLApp is declared as Excel.Application.

On a machine with Excel 2003, it finds the Excel 2003 application, not the
Excel 2007 application. Is there something that can be done so that the
Excel 2007 is found (without changing the code)? I know what I'd do so
this isn't a problem programmatically, but it probably affects 100 or more
folks and deploying a change is probably not the best option at this point.

Thanks,
Barb Reinhardt