the actual generic cli plugin uses a temp wav file for the source. You can pipe to the nero commandline encoder, but you will need the generic cli DLL from either the ogg vorbis aotuv b4 codec (the dll is 56.1KB IIRC) or the one from the musepack plugin (60.?KB), both of those generic cli DLLs support piping. Use one of those instead of the 64KB dll from the regular generic cli.
then edit the options file:
[Codec]
.m4a
neroaacenc.exe
[WriteWaveRIFF]
.....
the commandline textbox is here...
.....
then for the options you can type:
-q .4 -if - -of [OutFile]
then you can transcode without a temp file
I did this on my PC and added a combo box for bitrate, mode (lc, he, hev2), and quality.
But I find it to be a bit easier to just type the -q option, since there are so many possibilities
(note: add a space before the first argument in the commandline box, else it might not work)