I take it you tried that and it didn't work. Afaik you can send one such command... you could send multiple key presses that way but not multiple dial commands or request multiple xml pages.
So, you could go the hackish way: press key after key... first go off hook (press speaker key), then press the first key, second key, etc.. and with subsequent ipphoneexecute requests end dialing press the conference softkey (you gotta know at which position it's going to be so different softkey templates will make your life miserable) until you're all done.
Or there's the proper way: Use (J)TAPI to make two outbound calls and conference them together... It's quite a bit more effort but if you have your base CTI app working, turn it into a lib and you can re-use it and it will be a lot less work the second time around.
