I have 2 dedicated servers (A and B). Each server has a 10 mbps monthly bandwidth allowance. I am using 15 mbps on server A, and under 2 mbps on server B. All the bandwidth usage on server A is coming from a single domain.

Is there an easy way for me to serve some of the files from server A seamlessly from server B (without using redirects or subdomain)? I was hoping there's a simple solution that will let me use the spare bandwidth from server B instead of having to pay overages.

Thanks!

You could setup a duplicate of the web site on server b, and configure your dns zone to do a round robin between the 2. It means that you must use 1 db entry (in case you are using databases) and that you must have a way to share sessions between the 2 servers, but there is not much alternative than that.

Putting a static.domain.com url directing to the other server will only move most of the load to the second server.
You need a load balancer type setup here.

As you have dedicated servers, it should not be too hard to setup.
Basically (theorically, I never implemented this), you would have to have 1 server as the db, and you duplicate the vhost configuration and the files on the 2 servers.
Then, once they both work individually (you can play with tht hosts file to check it), you will need to update your dns zone file.
If you are using bind on your servers, then it's just a simple

www   IN  A   192.168.0.7
www   IN  A   192.168.0.8
www   IN  A   192.168.0.9

to declare every servers as answering to a subdomain.
Bind will then give a different ip destination to every request it got.

If you are using an outsourced dns server, then you might need to look with your hoster how to do that.