OK, so some more research reveals this example:

   <extension name="rtp_multicast_page">
     <condition field="destination_number" expression="^pagegroup$|^7243">
       <action application="answer"/>
       <action application="esf_page_group"/>
     </condition>
   </extension>

Then there's a suggestion of using a loopback:

<action application="bridge" data="loopback/3456/YOUR_CONTEXT/XML"/>

<extension name="rtp_multicast_page">
 <condition field="destination_number" expression="^3456$">
  <action application="set" data="absolute_codec_string=PCMU at 20i"/>
  <action application="set" data="jitterbuffer_msec=500:1000:20"/>
  <action application="answer"/>
  <action application="esf_page_group" data="234.5.6.7 23458 30"/>
  </condition>
</extension>
This is beginning to be in the right direction for what I want.

What I'm trying to do here is really aimed at callback. The user hits a web button and then Freeswitch pages his phone and then places an outbound call.

"api originate user/0095302 02070601234 XML dp0095"

Does the trick, by calling 0095302 and then on answer calls 02070601234.

What I'm trying to do is to not require the user to lift the handset and it has been suggested that paging is the way to do it. It's not a very true use of multicast, but might it work?