If you need to play the animation on a 3d object, why don't you just create a sprite sheet manually? tk2d does a lot of optimizations for sprites - you can place them in 3d space, etc, but if you wanna use the texture for a model its going to be a fair bit of work. They are in an arbitrary order, they will also be trimmed (transparent bits removed) and then they could be rotated too. To make this work on a 3d model wont be trivial.
I don't know what you're doing, but you could in theory play the animation into a rendertexture, and use that on the model...