We are using Blackberries to display PDF reports. Here are background details on the problem:
How about outputting the file to an RTF or an image file (JPG/GIF), and then viewing them in your web browser?
If that doesn't work well on the native browser, I would focus on viewing the file via some other web browser - for example, Opera Mini. I know for images it's easier to navigate "big" images in Opera Mini than the native browser.