In search of a Helmet-based steadicam solution for GoPro Hero 3
Unfortunately, the physics of a Steadycam require a counterweight (sometimes provided by springs) and distance to minimize the impact of movement by using the inertia of the system.  The best you might be able to do in a small size would be a shock mount.  If you had a power source, you could presumably put a small gyroscope in to try and further stabilize the rotation, but that would become pretty (very) expensive really fast.

A shock mount is probably your best option within a semi-affordable range and will deal with the actual movements forward and backward, up and down, etc, but not rotation.  It does appear that people have made multi-axis gyro mounts that would work, but they've all been custom builds and the power and weight is still probably prohibitive to wearing it in a run.  It would also still have to be shock mounted to account for lateral movements as the gyro would only deal with rotation.