I was fortunate to have the IPO services book my cruise for us. However, the following was posted some time ago on another board. I believe the procedure is the same for Wishes, and Wishes cruises are easier to come by. If this is out of date, perhaps somebody else will let us know:
You need to call 407-939-7529 exactly 90 days before the date you want to reserve. You can determine when to call by using the DIS's priority seating calculator if you CLICK HERE
Since these cruises are so much in demand, start calling about 6:55 am est. If you get a recording that they are not open yet, disconnect and immediately hit redial. If you get the recording thanking you for calling hit #3 right away, as soon as the second recording begins press #2, when the third recording begins press either your reservation number or phone number and finish with the pound sign. Then press #1, then #2. This will take you to a reservationist, if you have to hold do not disconnect or you go to the bottom of the queue.
When the reservationist answers do not make small talk, immediately tell him/her that you want to reserve the 8PM specialty cruise for such and such date.Do not ask to reserve an Illuminations cruise or you will waste time hearing that there is no such thing. After you get your reservation you can talk all you want, but these cruises are very difficult to reserve and seconds count when thousands of people are competing for only 5 boats.
When the reservationist indicates that you have obtained the reservation, tell him/her that you want to see Illuminations. He/she will then make arrangements for your cruise to depart the marina about 1/2 hour before Illuminations begins.
You will be told that they cannot guarantee that you will see Illuminations. They tell you this because, if Illuminations is delayed for any reason, your boat will still return to the marina at the end of your hour. So far, there have been no known instances where Illuminations was not seen.
If you have flexibility in your WDW itinerary, it is best to try to reserve a cruise for the first night you have available. That way, if you don't get the reservation, you can try the next day and the next, if necessary.
If you are unable to secure a reservation for an Illuminations cruise, do not give up. Cancellations happen every day. Keep calling and trying for that reservation, even when you are in WDW. I was told by a captain of one of these cruises that his boat has often sat idle because someone cancelled. You can snag a cancellation. I know, because I was lucky enough to get a cancelled cruise only 6 weeks before our trip last year.
I have also read about cruises being empty, so as a last resort, you could always show up at one of the docks and see if something is available. Good luck!!!
i'm sorry but I am not able to offer to share it because we are already full. 
