If the excel files are small, or your users have lots of bandwidth, you could pass the excel file back to the user in a hidden field, and use a refresh. If the hidden field has data, you pipe it back as an excel file.

Granted, this requires thrice the bandwidth, and you'd have to encode/decode the spreadsheet to fit it in the html, but it'd be relatively easy to implement ;). That said, I'd suggest finding a better approach.