From the Power IK Documentation, the Power IK Ground node does this:
For each Foot:
Calculate foot location in world space
Cast a ray from this location
If ray hits collider:
Smoothly move the effector towards hit point
Run solver using new effector locations
You can probably do this with the Full Body IK node, but you’ll need to handle smoothly moving the current effector to the new effector position based on the raycast.
So you’d have basically a function in your AnimBP for instance that does the raycasts based on your current foot positions, then lerps from the current foot/effector positions to the hit position.
Then you just need to feed those raycast hits as the effector transforms for Full Body IK node.