I did something similar with oracle reports some years ago.
- Run each report and save the output to separate files in an directory on the application server.
- Use functionailty from the iText-library to merge the pdf's into one file. This functionality has to be written in java and can be used on the application-server using the Java-importer in forms.
- Transfer the resulting pdf to the client using WEBUTIL.
- Show the resulting document using WEBUTIL's CLIENT_HOST
Hope this helps