This is done without breaking W6132 Annex YYYY draft MP3onMP4 which also uses AOT 29.
Samples:
http://samples.mplayerhq.hu/A-codecs/AAC/aacPlusDecoderCheckPackage_v2.1/bitstreams/File7.3gp
http://samples.mplayerhq.hu/MPEG-4/mp3on4/id5_1.mp4

Originally committed as revision 22281 to svn://svn.ffmpeg.org/ffmpeg/trunk