There doesn't appear to be an easy way to do this.
The component containing the colliders that would be involved in the collision is an InteractionBrushBone object. Unfortunately, these are spawned independently from the hand itself, and don't provide a reference to their owning hand.
The most straightforward workaround is probably to add a ParentHand field to the InteractionBrushBone class:
public InteractionBrushHand parentHand;
And modify the InteractionBrushHand class to set this field when it creates the brush bones, which occurs in the BeginHand() method (around line 108).
...
InteractionBrushBone brushBone = brushGameObject.GetComponent<InteractionBrushBone>();
brushBone.manager = _manager;
_brushBones[boneArrayIndex] = brushBone;
//add this line:
brushBone.parentHand = this;
...