I have to say that whole oggdec-tremor thing is nasty. When I did it back then a while ago I also had to try around a lot and have since then deliberately not touched this patched oggdec thing any more.
Maybe it would be a simplification to move a small patched oggdec into the mt-daapd source and have it compiled/installed when a –with-oggdectremor option is given at the ./confogure call?