There are ways to print multi-company financial statements. I'm not sure I'd use a report writer to create a financial statement, however.
If you want to simply show the financials for two companies in the same workbook you can create a macro to run the financial statement for each company and then automate Excel to merge the resulting statements. If you need to show Company A, then Company B and another that shows Company A+B then you have a little more work to do but it is still possible. There are third-party programs that make this easier: F9, for example. Accpac Intelligence might be able to do that but I haven't really worked with it much. Accpac Insight was born to do that.