It's been many years since I even touched AWS (seven or more, I think), but at one time you could upload an ISO of any arbitrary operating system install disk and provision your machines with that. They did provide common ones already mounted so you didn't have to deal with uploading. Perhaps they've changed, I don't know.
You might find useful stuff in this thread from two years ago: https://groups.google.com/forum/#!topic/comp.os.plan9/jLjaQZDe-H8 . I haven't really done more than superficially read bits of it, so beware.
I know you can run plan9 on ec2. This thread describes it. I have launched this AMI in us-west-2 before and successfully used drawterm to connect to it, but the latency made it unusable for me (I'm in NYC, so maybe if you are closer to Oregon your experience could be better?).
I have successfully used inferno in an AWS Workspace instance. I don't think you'd have a problem running it on an EC2 instance.
The venti in EC2 I am running now uses plan9port on an ubuntu box. The data is stored on an EBS volume attached to the instance. I use an SSH tunnel to connect there from my laptop and point vac to localhost.
I am toying with the idea of building a venti server that stores the blocks in something that spans multiple regions (cassandra and S3?) and opening it up to the world. Totally not practical, but I think it would be fun.
I'm a little late but i'll offer some input for completeness.