While I lack security and encryption knowledge beyond the basics I believe the answer is 'no'. I believe hosts can either access a VM's file system, RAM or SWAP.<p>You're better asking "How can I reasonably secure a VPS to make someone's life far more difficult."
There's no way to have a perfectly secure system if the hardware is in someone else's hands. Period.
See <a href="http://en.wikipedia.org/wiki/Blue_Pill_(software)" rel="nofollow">http://en.wikipedia.org/wiki/Blue_Pill_(software)</a> for one reason why.