Sorry for late reply, i was afk for some time 
that worked! (somehow)
i created 3 animations starting from my idle animation using “create animation from current pose”
- idle_to_AO_C
- idle_to_AO_L
- idle_to_AO_R
Inside each i added the additive settings referencing the single frame animation i previously created for the desidered pose.
i need the legs to be locked, but that’s another story i guess ahah!