In 15.5.1 we had an "Launch installed file" that ran as part of the Exit button on last installer screen.
a) the documentation on this is way out of date. A lot of the fields mentioned in the documentation no longer exist on that CA screen (see attached)
b) in 15.5.1 the "working directory" seemed to be implied to be wherever the installed file was launched from. In 15.8 it appears "working directory" is now "C:\Windows\System32" and there is no longer anyway to set a "working directory".
In the interim I'm going to change this in my install to a "Launch EXE with working directory".