As with most things in TG2, there are many ways to accomplish the stated goal of more explicit scene design. Creating terrains and masks in external applications is a common way, but you can also do a lot in TG2 with a bit of creative use of shaders.
For that particular scene I might just use the built-in Painted Shader and hook it up to a Displacement Shader, then paint the peaks directly. You ought to be able to make a fairly good rough out of the shapes, then apply some procedural displacement to it to get the details looking right. There are certainly more complex situations where this doesn't work as well, especially where erosion effects are needed (TG2's built in erosion only works on heightfields, and can be difficult to control).
- Oshyan
