...or you could simply put the animations into a B3D file, but load a version of your B3D with just the bones and no animation. Then manually load up bone key data, using sample code from here:
http://www.blitzbasic.com/sdkspecs/sdkspecs/b3dfile_utils.zip
It should then be possible for you to add animations together. If you apply the bone rotations and offsets from one key, you would then further rotate and offset bones using another key.
The idea of additive animation can be tricky, in terms of creating the animations, but with a little testing, I think this could work.
http://www.blitzbasic.com/sdkspecs/sdkspecs/b3dfile_utils.zip
It should then be possible for you to add animations together. If you apply the bone rotations and offsets from one key, you would then further rotate and offset bones using another key.
The idea of additive animation can be tricky, in terms of creating the animations, but with a little testing, I think this could work.