This is what I usually do,

I create two Excel files on the Workflow server; one for holding the data and another as an empty template:

• FileName
• FileName_Template

On the server I create and ODBC entry for the FileName copy, and then set that up as a data source for the workflow server.

Next, I create a placeholder document in my repository for the "report" in hidden folders we use for  process-specific things like that.

In the Workflow, I run the query first to collect the data, then I run a short Script activity that overwrites the "FileName" copy with the blank template to clear out any old data.

Next, I use a for each row activity and insert data to populate the excel file with the data from the query, then I attach the updated excel file to the "placeholder" entry in the repository.

Once that's done, I email file to the user by retrieving it from the repository entry.

The main limitation to this approach is that Excel files can only be accessed by one process at a time so this won't work if multiple workflows can potentially run on the same file in parallel.