Acabamos de descobrir que a seguinte sintaxe funciona:
jdbc:macromedia:oracle:TNSNamesFile=C:\\Oracle\\product\\11.2.0\\client_1\\network\\admin\\tnsnames.ora; TNSServerName=tnsentry
jdbc:macromedia:oracle:TNSNamesFile=C:\\Oracle\\product\\11.2.0\\client_1\\network\\admin\\tnsnames.ora; TNSServerName=tnsentry