NoData Value = 0, problem when creating NDVI, Erdas

I try to create an NDVI from Landsat and ASTER satellite images using Erdas Imagine. In Erdas, the satellite images have a nodata value of 0.

After creating an NDVI, the nodata value is still 0, but obviously there are also file pixels with the value 0 now (NDVI ranges from -1 to +1). So if I reset the NoData value to 0 (it is not done automatically), some pixels in my raster are missing since they are now classified as "nodata" 

Any suggestions?

Answer

I have found a workaround, but I hope there are better options. Before creating the NDVI, use Spatial Analyst/ IsNull tool with the satellite image to create a raster with two classes: data (=0), nodata (=1). Then create the NDVI and use the tool Spatial Analyst/ Con with the data/ nodata raster created before to change the nodata value to a number other than zero.

explanation in German: http://help.arcgis.com/de/arcgisdesktop/10.0/help/index.html#//009z000000ms000000

This works, but there must be better options!