Not as a normal, practical full-frame setup. Canon EF-S lenses are designed for APS-C bodies, and on a 6D they have two main problems: mechanical clearance and image coverage.

First, some EF-S lenses extend far enough into the camera that the full-frame mirror can strike the rear of the lens, risking damage. Second, even if mounted, an EF-S lens typically does not project a large enough image circle to cover the full-frame sensor, so you would get heavy vignetting or black edges.

The only workarounds mentioned are physical lens modification or using an extension tube. Modification is not considered safe, especially on full frame. An extension tube can create enough clearance and may enlarge the image circle somewhat, but you lose infinity focus and limit the lens to close-up work.

So for normal shooting, there is no safe, straightforward adapter solution. The practical answer is to use EF lenses designed for full-frame Canon bodies.