I found a very simple way to view BBM messages without marking the message with "R"
which makes you able to read messages and the sender will still think that you haven't as he/she will see the "D" instead
Go to BBM-->hit the blackberry button and select Options
Chat view---> Save Chat History (switch from Never to Device or Media Card)
now go to the chat that you want to view and hit the Blackberry button and choose View Chat History
now you'll read all the messages and the sender will think you haven't
some might find this useless or mean but it's not if you have annoying friends on BBM that you can't just delete but don't wanna let them see the "R" mark as that will make it even harder to ignore their messages lol