I aint any expert but think maybe your favourite
spatial denoiser would work with some kind of 'strength' arg to tune it.
(I like VagueDenoiser, but no idea if works well with SMDegrain [which I dont use])
EDIT: Actually, Removegrain(11) is similar to Blur(1.0), so I guess that you could use blur and vary with single float arg.
http://avisynth.nl/index.php/RgTools/RemoveGrain