There is not, sorry. You have two hurdles:
1) Separating the animation data from the rest of the data. JSON processing is easy, so getting only the animation data is straightforward. For binary you'd likely write a tool based on SkeletonBinary, read and discard bytes until the animation section is reached, then read and copy out the bytes for the animations.
2) Loading only the animations, using an existing SkeletonData. You could modify SkeletonJson or SkeletonBinary for this. There is already a readAnimation
function, it is just not exposed.
You'll have to take special care not to modify the skeleton, else loading the animations will fail spectacularly. Sending the whole skeleton would have to be significantly larger than sending only the additional animations, else this would not be worth the trouble. That is the case in most scenarios, since bandwidth is plentiful and skeleton data is small. Be sure to send your skeleton data as binary with compression (deflate is generally good enough).