I created a simple bean for my static parameter and add
ExecutionContext executionContext = smooks.createExecutionContext();
MappingStaticParams staticParams = new MappingStaticParams();
staticParams.setSomeTextParam = "someValue";
BeanId beanId = executionContext.getBeanContext().getBeanId("staticParams");
executionContext.getBeanContext().addBean(beanId, staticParams );
This puts the bean in scope for my smooks filter config file which can use a jb expression to map the parameters:
<jb:expression property="staticText">staticParams.someTextParam</jb:expression>