Hi Joshua,
I’m not sure if it would fit in your workflow, but you can enable Face (or Vertex) Selection Masking in Weight Paint Mode:

(that disables the Bone Selection, but you can Select those in the Vertex Groups list):
You can then, for instance Box Select one leg in Edit Mode, and then you only Paint in those Faces. Youu can also Select the Faces you want to Paint on in Weight Paint Mode, but then you’d have to be aware that, for instance Box Select, only Selects what you see.