As far as I know, the above is the only way to do what you're asking. But note that Keynote is $10 and the Keynote remote app for iPhone is $0.99. Also, opening ppt/pptx files in Keynote isn't a science - there are font differences, symbols display weird, transitions may or may not work...you need to be ready to go back-and-forth a few times until you see in Keynote what you have in Powerpoint.
Having said that, I have had no problems in getting bluetooth to work between the iPhone and the iPad. But I have heard of others having this problem too. If you can get WiFi it's faster anyway, but I don't have that option at my workplace.
Good luck!