You could start by isolating the background element with "View selection in 3D" from the context menu.
Now set your construction plane by picking the face where you want to draw.
Set view mode to Axonometric.
Now go to View > 3D Navigation Extras > Look to perpendicular of clicked surface.
You can now draw on the surface of the background element using the Morph tool.
Apple iMac Intel i9 / macOS Sonoma / AC27UKI (most recent builds.. if they work)