Creating Call Back VIs without using the utility is very, very difficult. It did not even occur to me that you were not doing it this way. As a note, you can pass data into the callback by bundling it together and sending it to the User Parameter terminal. If you decide to change the cluster later, you will need to recreate the callback VI. You can save time in this case by control-c on all objects in the old VI and control-v in the new VI.
Have fun with the callbacks. They are really cool.
