FBX multitrack animations (multi take) into single track - possible?

I have a .fbx file which i’ve previously used in Unity a long time ago. It has many animations stored in multitrack. When i import this to Unity, all animations are there, so the file is ok. Now, i want to fix and enchance some of the animations (****, about 2 years ago i thought they looked good :D), but i can’t import them into Blender (as far as i know, Maya and 3dsMax also doesn’t support multitrack fbx) - after importing, it shows only the first animation.
Is there some software to convert multitrack .fbx to a single track file? To somehow extract these animations, to be able to edit them in 3d package?