Spine doesn't use animation clips (nor Mecanim), and has no root motion support itself.
I get around this by placing a rootMotion bone between the Spine skeleton's root and the rest of the skeleton. Animate this bone (translations only) for your root movement, then re-parent the skeleton to the root bone proper whenever you export... this shouldn't break your animation (disclaimer: I can only account for personal experience! Do tests first), and you can re-parent the skeleton to the rootMotion bone whenever you need to go back to editing it. It can get a bit messy if you forget to do this then edit your animation, as it may throw your root motion sync if i.e. a foot or pelvis gets moved, but you can always re-parent and tweak.
You can then read the root motion from the rootMotion bone in your animation code, i.e.
Spine.Bone rootMotionBone = skeleton.FindBone("rootMotion");
float x = rootMotionBone.x;
Remember rootMotionBone's positions are absolute, and resets at the loop, so you need the difference (i.e. Mathf.Abs()) between frames, and a catch for the loop reset.
Not especially elegant, but it's functional, and allows you to switch between Root and In-Place motion with zero hassle.
Native support for root motion would of course be a big bonus.
