Okay, so that clears it up a bit...
The difficulty here is that the ac, using this method, you will intercept the ILS beam, perhaps 'at or above', then the ac will drop, to re-acquire the beam, especially when using baro-vnav to ILS intercept...
I was just wondering how the FMC calculate the VNAV path when you put the extended centerline (FAP with the intercept course equal to the localizer course) when you are under radar vector for an ILS approach.