One option, here is the general code logic:
Create a script tool with a Field multi value data type
Within the python code, loop through the field list and define the index value as the field parameter within the IDW method
fieldList = arcpy.GetParameterAsText(0)
fieldList = arcpy.GetParameterAsText(0) for fieldName in fieldList.split(';'): outIDW = Idw(inPointFeatures, fieldName, cellSize, power, searchRadius) # Save the output outIDW.save("C:/temp/idwout_{0}.tif".format(fieldName))