George,
A technique that I have frequently used is to create a regular VI, place an indicator of the appropiate data type, wire a block diagram constant to the indicator, wire the indicator to an output terminal, and give the VI an icon (and file name) indicating that it is a constant. You can then place this VI anywhere and if you ever need to change the value, you can change the constant in the VI and it will be changed everywhere. For multiple #defines, you can use multiple VIs or put several related constants into a single VI.
Regards, Aaron
