The HP Motion Controller Plugin for Unreal has Action Mappings for "HP Mixed Reality (R/L) Thumbstick X/Y" that fire at full thumbstick travel. But it only fires in the positive X/Y directions. Full stick in the negative X/Y direction does not fire this event. If it fired at both limits you could look at position and figure this out but it does not.

However these should probably be changed to separate inputs for "(R) Thumbstick Up" "(R)Thumbstick Down" "(R) Thumbstick Left" "(R)Thumbstick Right" . This would follow conventions for all other motion controller mapping in Unreal.