Change your 3D View drawtype by clicking on the menu that looks like one of these:
Change it to Textured (the first one) so you can see your mesh's assigned image wrapped around it.
Create a new image, size 256 x 256 or 512 x 512 and assign it to your mesh. Find the Bake tab and bake Ambient Occlusion instead of Textures. Save your new shadow map.
Paint a texture with your shadow map in your image editing software of choice.
Before we begin, I want to change the draw type in the 3D View to Textured. Find the small menu to the right of the Mode menu (marked in red - click the image to enlarge) and switch the draw type to Textured. If your sculptie is currently assigned a UV texture (such as a sculpt map), you'll see that texture placed onto your mesh in the 3D View.
If you've ever worked with other Blender sculptie templates, you may already know how to bake textures onto an image. However there are other types of images we can bake. The type we're going to bake now is Ambient Occlusion - or global shadows.
First we want to assign our mesh to a new texture. If you have multires on your mesh, you need to switch to Level 1 or Apply Multires before you change textures. Then go into edit mode and select All, by tapping A until all the vertices are yellow and the faces pink. Then in the UV/Image Editor, go to the menu Image > New. Make a new image that's 256 x 256 or 512 x 512. Hit OK. (If you switched to Multires level 1, you can now switch back to level 3)
Now go to the Scene > Render Buttons (marked in green - click the image to enlarge) and then find the Bake tab (blue) and change the bake type to "Ambient Occlusion" (yellow) and hit Bake. Wait a few moments for Blender to bake shadows onto your image. Save the image as something meaningful.
Usually this shadow map gives you enough 'landmarks' on the texture to be able to paint a texture that exactly fits your sculptie. Just use your favorite image editing software.
If you get black lines running through your shadow map, like the image above, this is something that happens in Blender sometimes, especially if there are faces on your sculpt that are twisted. Either paint these out, or blur them, or find some other means to get rid of them in your image editing software.