In addition to the aforementioned attempts, today I also tried adapting a virtual file system plugin as a way to run my script from the Modifiers section. After building a vfs sandbox, this is what i used:
// JScript - vfs sandbox Log file proves call to vfs sandbox occurs:
var fsutil = DOpus.FSUtil;
var items = fsutil.Exists("gary://FOO_123_JSCRIPT");
DOpus.Output(items);
// CLI - vfs sandbox Log file proves call to vfs sandbox DOES NOT occur:
Exists("gary://Foo_123_EVAL")
// Modifiers section of a button using JScript.
// vfs sandbox Log file proves call to vfs DOES NOT occur:
@eval: test=Exists("gary://FOO_123_JSCRIPT")
@enableif:test
So I am giving up on getting a Dopus UserCommand to execute from the Modifiers section of a button having Jscript code.
Thank you everyone for your input and help!
Additional Info: