Triplanar projection is totally doable, here is an example in UDK : 3d projection texture coordinates for Terrain layers - Epic Games Forums
Basically, you just have to get the WorldPosition node, mask out only two components (since you want UV coordinates) and scale a bit the result before plugin it in your texture sample. Note however that for normal maps it will not work properly. Since your are not anymore in the UV space of the mesh/landspace, you can’t rely on its Tangent/Binormals.