[CMake] Adding (external project) dependency to interface target

[Jose Gonzalez]

My project uses the "external project" functionality to download and
install a "headers-only" library. I use an "interface library" to import
that library dependency to my project. I'd like to add a dependency from
the external project target to the interface library to trigger the library
downloading and configuration process.
But apparently this is not allowed and I get this error:
add_dependencies Cannot add target-level dependencies to INTERFACE library
  target "EigenExternal"

Is there any workaround for this or am I doing something wrong?

Thanks a lot,
Jose
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://www.cmake.org/pipermail/cmake/attachments/20140426/9da726cf/attachment.html>