Using ExternalProject_Add with catkin

edit

I've been trying to add an external project to catkin using the ExternalProject_Add feature in CMake. My CMakeLists.txt files looks something like follows:

cmake_minimum_required(VERSION 2.8.3)

include(ExternalProject)

ExternalProject_Add( foreignproject
  PREFIX foreignprojectlib
  GIT_REPOSITORY foreignproject.git
  BUILD_IN_SOURCE
  BUILD_COMMAND cmake --build .
  INSTALL_COMMAND ""
)

project(rosproject)

catkin_package(
  INCLUDE_DIRS include ${DIRECTORY_TO_FOREIGN_PROJECT_HEADERS}
  LIBRARIES rosproject foreignproject
  CATKIN_DEPENDS opencv2 roscpp tf
  DEPENDS system_lib
)

include_directories(include
  ${catkin_INCLUDE_DIRS}
)

add_executable(rosnode src/rosnode.cpp)

The problem I am coming across is that the header file from the external project is not being found. In fact, I'm finding that catkin_make (-j1) tries to build rosnode before it builds the external library. Could someone explain the proper way of using ExternalProject_Add or post an example of a CMakeLists.txt file that successfully uses ExternalProject_Add?