Hi!
The best way to do that is:
Declare a Rundeck-wide global execution variable in the framework.properties
file:
a) Stop the Rundeck service.
b) Open the framework.properties
file with your favorite text editor and add this line: framework.globals.rundeck_path=/your/rundeck/path
then save it.
c) Start the Rundeck service.
In your job, define the remote option in the following way: file:${globals.rundeck_path}/options.json
Now you can use that global execution variable as the $RDECK_BASE
shell env var.
Take a look at this to get more info.
Hope it helps!