Have you used the "Edit 2D pictures" option in Bryce? You can make a custom texture or apply a picture onto a figure or 2d plane. That's how I get the East Asian roof tiles on my buildings. Here's how to use alpha planes:
1. Get a picture file. It can be bmp or jpg format; doesn't really matter.
2. If you want the object to take a specific shape (like a tree or humanoid, for example), then you need to create a transparency map. The figure should be completely white and the background (what should be transparent) should be all black.
3. Open up Bryce. Click on the icon of the naked guy with four arms and four legs (it should be called "Create Picture Object"). It should take you immediately to the "Edit 2d Pictures Option."
4. The interface should show three large square slots on the upper part and tiles of image slots on the bottom. Click on an empty slot in the image slots below to create a new image. The slot on the left is for the regular picture. The slot in the middle is the transparency map. Once you load up your picture in the left slot, load up the transparency map for the middle slot. Then create the image and you should have your cardboard cut-out.
You can do this for any 3d figure, but 2d planes are better to work with since the texture will simply repeat like tiles on a 3d figure.