I've done it - but it involves some messing about. I'm thinking of producing another short utility to do all the steps quickly in one program.
I did the following:
1. Recalculate the UV data so that one limb corresponds to the square [0,0.5]x[0,0.5] and the other to the square [0.5,1.0]x[0.5,1.0].
2. Save the revised object as a single mesh.
3. Resize the source images so they are the same dimensions, e.g. 512x512.
4. Combine the two source images, i.e. the bark and leaf textures, so that one corresponds to the top left of the new image and the other to the bottom right, i.e. so they match the changes to the UV data. Then fill in the rest of the image with something sensible.
5. Create suitable .bmp thumbnail and .fpe files.
6. Put everything in a sensible folder in the entitybank and away you go.
Here's a screenshot with such a model that I posted somewhere else: