It is not possible at the moment. Only developers can do it if they include the code into their product.
Umberto told that possibly it will be implemented to add the feature yourself for other aircraft as well, but at the moment you can not do that if you don't have a program to change the variables.
This is not entirely correct. You do not have to be a developer. Anyone can do it themselves if they have a basic knowledge of xml code. You also do not need any special program to write the code.
Notepad is quiet sufficient. I was prepared to share my own code using the GSX L vars until I started being insulted by members on this forum.
Anyone interested in attempting xml code, I suggest they visit the following sites:
www.fs2x.com/tutorials.htm, Avsim.net (Textinfo Gauge 4.0 and XML Tutorial).
The FS Developer site also has hundreds of examples to help getting started.
This is my final word on the subject and await further abuse from non-believers.
Eisbahn