No, it is not possible in LabVIEW 6.0.2 or lower. I have read that it can be done in CVI and then exported to LabVIEW. If I had to guess I would probably say it was Jeane-Pierre Droilet (?sp), or Dr. Scott Hanna (?sp), or Rolf Kalbermatter (?sp) who posted a method for accomplishing this task.
If you are interested in finding out how this was done I suggest you use Brian Renken's Search engine at http://www.searchview.net/ to find the posting (it was posted in 2000 or 2001 I think). I believe they are called "sparse enum's".
If you want to accomplish a similar functionality with pure "G" you could use a translator type sub-VI. The translator would use the use the enum value to index an array of constants that has the "Sparse-enum"s you want returned. An advantage of this method can be realized if the translator is implemented as an action engine where the "indexed-array" is read from an un-initialized shift register. This would allow redifining the enums "on-the-fly.