Draw objects temporarily without adding them, but show as "part of scene"

Scripting
1

I’m working on a grasshopper script where we are listening to a signal (via an event listener), and that signal will cause a geometry to be shown on the canvas. I want to avoid expiring a component everytime and use a preview component, but rather just subscribe to the signal and manually add the geometry to the display pipeline.

But I’m very much in doubt how.

Below is a code snippet where I show a sphere, but it, as the function also suggests, is drawn on top of everything. How can I ensure that it is “part of the scene”?

import System
import Rhino
import Grasshopper

import rhinoscriptsyntax as rs
import Rhino
import scriptcontext as sc
import System.Drawing as sd


class MyComponent(Grasshopper.Kernel.GH_ScriptInstance):
    def RunScript(self, pt: Rhino.Geometry.Point3d, radius, show, clear):

    # Create the conduit once and stash it so it survives across runs
        if "sphere_conduit" not in sc.sticky:
            sc.sticky["sphere_conduit"] = PersistentSphereConduit()
        conduit = sc.sticky["sphere_conduit"]

        if clear:
            conduit.Enabled = False
            sc.doc.Views.Redraw()
            return "Cleared"

        if show:
            conduit.update_sphere(pt, radius)
            return "Drawing at ({:.1f}, {:.1f}, {:.1f})".format(pt.X, pt.Y, pt.Z)

        return "Idle"


class PersistentSphereConduit(Rhino.Display.DisplayConduit):
    def __init__(self, colour=sd.Color.CornflowerBlue):
        super(PersistentSphereConduit, self).__init__()
        self._mesh = None
        self._mat  = Rhino.Display.DisplayMaterial(colour, 0.8)

    def update_sphere(self, centre, radius=1.0):
        sph        = Rhino.Geometry.Sphere(centre, radius)
        self._mesh = Rhino.Geometry.Mesh.CreateFromSphere(sph, 16, 16)
        self.Enabled = True
        sc.doc.Views.Redraw()

    def CalculateBoundingBox(self, e):
        if self._mesh:
            e.IncludeBoundingBox(self._mesh.GetBoundingBox(True))

    def DrawForeground(self, e):
        if self._mesh:
            e.Display.DrawMeshShaded(self._mesh, self._mat)