There are two reasons why this can't work as explained:
1- A built application can't build an application because VIs have to be edi¬ted, compiled and saved in the building process. Either operation can't be done in Run-Time Engine.
2- "_Build Application from Script.vi" can't be built into an application since it uses VIs that are loaded in memory by the Application Builder.
However, one can build an application that reads the script file from the command line and invoke LabVIEW (development) with VI Server to Call "_Build Application from Script.vi" with the script file parameter.
That is a great step forward that we have now natively in LabVIEW what was the core of the OpenG Application Builder (not to blow my own trumpet, of course...¦
¬)