JBoss does invocations through the MBeanServer for all sorts of things and the overhead is affortable.
You could create a private MBean registry of yours, that works behind the scenes, but then you'd loose all the benefits of de-coupled invocations.
You probably need to benchmark to make a decision.
I thought I heard somewhere (and maybe someone can confirm) that a version of the JBoss Agent had been created that used AOP for invocations instead of reflection. The results were not measurably better.
After Java 1.4, I think reflection performance is no really an issue any more.
AOP uses reflection, too, if I'm not mistaken