Question Skinned character plus Rig and bone animation !?

Hi,

i am trying to create a rig for a driving avatar using a mixamo model... the model is OK but it has the fingers straight which i want to key in bent position in animation clip... i also have IK constraints for both left and right arms ( from upper arm to wrists without touching the fingers ) and while i am having IKs added to the arms, Unity doesn't allow me to keyframe the fingers ( they just pop back at original position ) !

Is it possible to still animate part of the bones ( which do not use any constraints ) when using a Rig or we suppose to animate the rig controls only ?

Thanks !