you're out of luck I'm afraid. You cannot override the meshing settings in Grasshopper preview yet. You'll have to bake the objects, take your snapshot/frameshot then delete them again. There is at least one VB components floating around which does this automatically (it bakes some geometry, calls the _Render command, then the _SaveRenderWindowAs command, then deletes the geometry again), but I no longer have a copy of it on my laptop.
err... I`m worry if we a re talking about different things - i want to get a picture/animation of my geometry shaded parametrically in ghp in hi-resolution.
... or i cant understand you...(