I know this is old but I was looking for the same answer and this is what I’ve come up with:
I have sheathe and unsheathe sword anims (as well as attacks) and they look great when idle because the character’s legs widen nicely getting ready for combat, but of course I wanna make the char able to unsheathe (and attack) while running, So…
Make your anim montages, change the DefaultSlot in them to Upperbody
in the ABP, make a saved cache pose for MainStates
Use cached pose Main States and from it, use Layered Blend Per Bone
Duplicate a Cached pose for MainStates abd from it, use Slot DefaultSlot, then click the DefaultSlot node and change it to UpperBody in the details
Connect the UppserBody slot node to Blend Poses 0 in the layered blend ber bone node
Select the LBPB node and in the details, go to Layer Setup/Branch Filters and add an Array element
Drop it down and in Index 0, use “spine_01” (If using SK_Mannequin, otherwise use whatever base spine bone name that your skeleton uses)
From the output pin on the LBPB node, use a Blend Poses By Bool node
Use another cached pose MainStates node and from it use another Slot UpperBody node
Connect the UpperBody node to the False Pose pin
In your variables list, drag out a ShouldMove boolean that comes with ABP_Manny. You can also use GroundSpeed and use a Greater Equal node and use like 0.5 for the float value it should be greater or equal to. Connect either one of those nodes to the Active Value pin in the Blend Poses By Bool node
From there, you can connect the Blend poses by bool output pin to your OutputPose node, or to the ControlRig node that checks for Should Do IKTrace, which then goes to the Output Pose node
I should say that I dont fully understand why/how this works lol. Especially the Blend poses b ybool False Pose pin being connected to the MainStates using the UpperBody slot node. IF character is NOT moving, why would it use the UpperBody Slot? Either way, this is what I have found and this works for me. Maybe it will help someone else in another 3 years lol