It is possible. Check out this guide for SR:TT:
http://www.saintsrowmods.com/forum/threads/custom-radio-stations-guide.2/
There are a few things to pay attention to:
1. You have to use the new tools for SRIV for extracting and building the packages.
2. to use ww2ogg you have to use it with the command switch "--pcb packed_codebooks_aoTuV_603.bin" ("ww2ogg.exe radio_k12_media_00000.wav -o radio_k12_media_00000.ogg --pcb packed_codebooks_aoTuV_603.bin" for example), so you can't just drag and drop the files.
3. To convert your own song you have to use the new Wwise tool from 2013, not the one from 2010. You can find it here:
https://www.audiokinetic.com/downloads/