In case anyone happens on this with the same issue, I was able to overcome it.
After re-reading @Paint_Ninja's last post numerous time, it finally dawned on me that he was referring wholly to the forge installer, which has nothing to do with the packaged modpack installer. As such, I downloaded the new copy of the forge installer and copied it to my linux host, then opened a second ssh session and prepared a cp command to move the new (correct) installer over to the install directory where I was installing the modpack. After the modpack installer had just about finished retrieving files, I overwrote the installer.jar file with the correct one in a seperate ssh session.
The modpack (packaged) installer then used that jar to install forge with the included files, and the install finished as I would have expected.
Thanks all!