I'm the OP and now answering my own question. It turned out that I was over complicating the whole thing and FreeSWITCH is extremely intuitive to use. Simply setting a channel variable
originate {callee_2=2223334444}sofia/gateway/myProvider/1112223333 &ivr(my_ivr)
and accessing the channel variable in the ivr xml
<menu name="my_ivr"
greet-long="say:Thank you for filling out the form."
greet-short="say:Thank you.
......
digit-len="4">
<entry action="menu-exec-app" digit="1" param="bridge sofia/gateway/myProvider/${callee_2}/>
</menu>
will do the trick. Hopefully it helps.