arcgis desktop - focal statistics with variable radius

is there an easy way to do focal statistics on a raster, with a variable radius for the neighbourhood to be searched? As in: that search radius would be stored in another raster?

i tried something like

f_max = arcpy.sa.FocalStatistics(Tau,arcpy.sa.NbrCircle(rad_ras,"CELL"), "MAXIMUM","DATA")

it returns

Traceback (most recent call last):

  File "K:\Informatik\tools\arcpy\GKPROZ\test_3.py", line 383, in 
    ufereros_gq(r"F:\25sg\25107\TG7\access\gis_logger_tg7.mdb",gq_nummer, False)
  File "K:\Informatik\tools\arcpy\GKPROZ\test_3.py", line 300, in ufereros_gq
    f_max = arcpy.sa.FocalStatistics(Tau,arcpy.sa.NbrCircle(rad_ras,"CELL"), "MAXIMUM","DATA")
  File "C:\Program Files (x86)\ArcGIS\Desktop10.0\arcpy\arcpy\sa\Functions.py", line 4796, in FocalStatistics
    ignore_nodata)
  File "C:\Program Files (x86)\ArcGIS\Desktop10.0\arcpy\arcpy\sa\Utils.py", line 47, in swapper
    result = wrapper(*args, **kwargs)
  File "C:\Program Files (x86)\ArcGIS\Desktop10.0\arcpy\arcpy\sa\Functions.py", line 4783, in wrapper
    neighborhood = Utils.compoundParameterToString(neighborhood, ParameterClasses._Neighborhood)

  File "C:\Program Files (x86)\ArcGIS\Desktop10.0\arcpy\arcpy\sa\Utils.py", line 75, in compoundParameterToString
    return str(parameter)
  File "C:\Program Files (x86)\ArcGIS\Desktop10.0\arcpy\arcpy\sa\ParameterClasses.py", line 202, in __str__
    self.units])
  File "C:\Program Files (x86)\ArcGIS\Desktop10.0\arcpy\arcpy\sa\CompoundParameter.py", line 39, in _toString
    userProvidedPounds = [value == "#" for value in values]
  File "C:\Program Files (x86)\ArcGIS\Desktop10.0\arcpy\arcpy\sa\Functions.py", line 3598, in EqualTo
    in_raster_or_constant2)
  File "C:\Program Files (x86)\ArcGIS\Desktop10.0\arcpy\arcpy\sa\Utils.py", line 47, in swapper
    result = wrapper(*args, **kwargs)

  File "C:\Program Files (x86)\ArcGIS\Desktop10.0\arcpy\arcpy\sa\Functions.py", line 3595, in wrapper
    return _wrapLocalFunctionRaster(u"EqualTo_sa", ["EqualTo", in_raster_or_constant1, in_raster_or_constant2])
RuntimeError: ERROR 000732: Input Raster: Dataset # does not exist or is not supported

although the raster(s) exists. I assume this means that the Nbr function can't work with a raster, as the same line works fine for a fixed value for the radius of the circle. I have found a workaround in that i do the focal statistics 10 times with a different radius each time and then use arcpy.sa.Pick to choose from those 10. This is however painfully slow. Is there a better way to do it?

any help would be appreciated.

i use ArcGis 10.0 SP4 on an info license on Windows 7 64