Question How can I remove the hierarchy root restrictions for constraints?

Hello,

I am trying to make a character with customizable size, who uses a weapon that will not change in scale despite the character's scaling.

I want to use animation rigging's multi-parent constraint in order to make the weapon be properly held, but...
Because the character's hierarchy is scaled (as part of the customizable sizes), this affects the weapon.

I'd like to be able to have the weapon disconnected from the hierarchy of the character, but still be evaluated with rig graph.

Is there any way I can remove the 'it must be under the rig builder hierarchy' restriction? I can mess with the playablegraph if necessary but I'd like some outlining of what to do, please.