The only way possible is to get an external device to play the recordings over the PA. Something like a Viking DNA-510 is what you are looking for. You put it in as a trunk or analog extension on the system, analog station would be easiest. As an analog extension you just call the extension and enter the announcement number you want to trigger and it will play over the PA.
Got couple of more question on how it works.
What kind of announcement is going to use, is it the Direct Page or the Loudspeaker Paging?
Once i set it up as an analog line, how do you do the paging? If I call the extension and it starts playing the recorded message and then dial the announcement number. Would it put the analog line on hold and i'll be at the part where I can do the loudspeaker paging?