I think you are heading down a dead-end. You will never have enough control over the rendered output from SSRS and any solution will be fragile.
I assume the SSRS data source is SQL or some other source that Excel can read. I would take the Dataset code from the SSRS report and implement it as Data tables in Excel, e.g. Data ribbon / Get External Data.
In the simplest implementation, each query just populates an Excel Table. You can set the connection definitions to auto-refresh on open.
For more complex requirements you can build an Analysis Model in Excel using the Power Pivot Add-In (included (but not enabled) with Excel 2013). This lets you relate datasets to each other and add calculations etc. The gotcha here is that you cant auto-refresh without SharePoint.