I am not sure how one would go about that.
You would want to create a new instance of the Crystal report viewer, set the report source to the correct report and the datasource to the Excel, and any parameters to the correct values and then 'Show' the report viewer, at least those are the steps I believer one would need to complete to display a report in .Net... I would assume they would be similar in VBA, but I don't know if all of that is possible.
Sorry I can't be of more help.