Hi,
Please check out page 32 of the "Viewing Documents Using OpenDocument ■ SAP BusinessObjects Business Intelligence platform 4.1"
You want to use sOutputFormat=P "to Specifies the format in which to open sOutputFormat the target document."
For example,
http://<servername>:<port>/BOE/OpenDocument/opendoc/openDocument.jsp
?iDocID=Aa6GrrM79cRAmaOSMGoadKI&sIDType=CUID&sOutputFormat=P
Hope this helps,
Jin-Chong