Busy File

Hopefully this is simple. I have a rule structure set up to "backup" spreadsheets each time I save them. More precisely, the rule will copy the saved file to a specific backup folder with the date/time appended to the front of the name.
The structure and rules work just fine. The problem I am encountering is that the files are usually open in excel when I save them. I would still like Hazel to copy them over to the backup folder as the files are copiable from the terminal or finder and open just fine in excel. However, because they are open, the Hazel log shows the file as "busy" and skips the copy. This totally defeats the idea. Is there a way to make hazel proceed?
The structure and rules work just fine. The problem I am encountering is that the files are usually open in excel when I save them. I would still like Hazel to copy them over to the backup folder as the files are copiable from the terminal or finder and open just fine in excel. However, because they are open, the Hazel log shows the file as "busy" and skips the copy. This totally defeats the idea. Is there a way to make hazel proceed?