As they are hosted on EC2 couldn't you use Amazon Cloudfront with them without too much trouble and with no latency issues? http://aws.amazon.com/cloudfront/
The main issue would be integrating Cloudfront with Rails not getting it to run on Heroku. (A quick search doesn't show much support for using Cloudfront with Rails in general)
The main issue would be integrating Cloudfront with Rails not getting it to run on Heroku. (A quick search doesn't show much support for using Cloudfront with Rails in general)