Please post user requests on the user forum.
JBoss AS is not designed for use as an HTTP proxy loadbalancer. There used to be (I believe in 4.0.4 and earlier) a load balancer web application someone contributed that would do this (look in the varia module of the source distribution) but it wasn't maintained and was never the recommended solution for load balancing vs. mod_jk. It didn't have any association with the remote Java client load balancing policies you mention.
mod_jk doesn't just support a round-robin approach; the recommended configuration uses sticky sessions, which has semantics similar to the FirstAvailable load balance policy.