What's The Best Way To Include AnimationClip In AssetBundle?

In order to re-use the animationclip and for some other purpose, we put every single animtionclip in separate fbx files.(eg. monster@run.fbx,monster@stand.fbx).When we build the fbx files into assetbundle,it seems not only include animationclip.(we tried a lot different import setting,like not create avatar、optimize game
objects(hide transforms,but the assetbundle file's size is always bigger than just build from a .anim file).So is there anyway to just include the animationclip from fbx into assetbundle? Or need to copy the animationclip(Crtl+D) to a .anim file and then build it to an assetbundle?(in that way we will lost the controll to change setting with it).