I was just now testing your elements widget in master
OS: Ubuntu 14.04.1 LTS
Word size of OS: 64-bit
Word size of FreeCAD: 64-bit
Version: 0.15.3976 (Git)
Branch: master
Hash: f647f254903047d7b410e878fbf465f91021b654
Python version: 2.7.6
Qt version: 4.8.6
Coin version: 4.0.0a
SoQt version: 1.6.0a
OCC version: 6.7.1
I just realised that it does not support external geometry. It does support construction mode elements, but not external geometry linked elements.
I have created a feature request and assigned it to you....I hope that is OK with you...if not I will unassigned it.

Jim