This is covered in the documentation.

You need to declare an ejbSelectGeneric method in your deployment descriptor and can then call it with the actual JBossQL query string that you create at run-time.

<jbosscmp-jdbc>
<enterprise-beans>
<entity>
<ejb-name>MyEJB</ejb-name>
<query>
<query-method>
<method-name>ejbSelectGeneric</method-name>
<method-params>
<method-param>java.lang.String</method-param>
<method-param>java.lang.Object[]</method-param>
</method-params>
</query-method>
<dynamic-ql/>
</query>
</entity>
</enterprise-beans>
</jbosscmp-jdbc>