*env
Build Configuration:
BB_VERSION        = "1.19.0"
BUILD_SYS         = "x86_64-linux"
NATIVELSBSTRING   = "Fedora-17"
TARGET_SYS        = "i586-poky-linux"
MACHINE           = "emenlow"
DISTRO            = "poky"
DISTRO_VERSION    = "1.4+snapshot-20130527"
TUNE_FEATURES     = "m32 core2"
TARGET_FPU        = ""
meta              
meta-yocto        
meta-yocto-bsp    = "hongxu-0524:e8197722de1f6006ceae0d4266de91c1db7278e3"
meta-intel        
meta-emenlow      = "master:2c9fb03aad0108f3ff2713de568632a117227c10"

*problem
1, The destro didn't install scons: 
$ which scons
/usr/bin/which: no scons in (/buildarea2/hongxujia/poky/scripts:/buildarea2/hongxujia/poky/bitbake/bin:/usr/local/bin:/usr/bin:/usr/local/sbin:/usr/sbin)

2, build python-scons-native
$bitbake python-scons-native

3, start a devshell
$bitbake gzip-native -cdevshell

4, invoke scons in the previous shell, import module `SCons.Script' failed:
$bash-4.2$ scons -h
Traceback (most recent call last):
  File "/buildarea2/hongxujia/build-20130520-udev-emenlow/tmp/sysroots/x86_64-linux/usr/bin/scons", line 188, in <module>
    import SCons.Script
ImportError: No module named SCons.Script

*analysis:
1, While building scons as default, scons's lib will be install in the dir of `scons' or `scons-2.3.0' if the option `--install-lib' is not set explicitly.
See tmp/work/x86_64-linux/python-scons-native/2.3.0-r0/scons-2.3.0/setup.py, line 241:
241         if not set_explicitly("lib", args):
242             # They didn't explicitly specify the installation
243             # directory for libraries...
244             is_win32 = sys.platform == "win32" or args[0] == 'bdist_wininst'                               
245             prefix = get_scons_prefix(self.install_dir, is_win32)                                          
246             if Options.standalone_lib:
247                 # ...but they asked for a standalone directory.                                            
248                 self.install_dir = os.path.join(prefix, "scons")                                           
249             elif Options.version_lib or not Options.standard_lib:                                          
250                 # ...they asked for a version-specific directory,                                          
251                 # or they get it by default.                                                               
252                 self.install_dir = os.path.join(prefix, "scons-%s" % Version) 

2, While build python-scons-native, `--install-lib' is explicitly set, and scons's lib was not installed in the dir of `scons' or `scons-2.3.0'.
See meta/classes/distutils.bbclass, line 41:
 35 distutils_do_install() {
 ...
 41         ${STAGING_BINDIR_NATIVE}/python-native/python setup.py install --install-lib=${D}/${PYTHON_SITEPACKAGES_DIR} 

3, While invoke scons-native, the scons searches the lib in ${STAGING_DIR_HOST}/${PYTHON_SITEPACKAGES_DIR}/scons, ${STAGING_DIR_HOST}/${PYTHON_SITEPACKAGES_DIR}/scons-2.3.0 rather than ${STAGING_DIR_HOST}/${PYTHON_SITEPACKAGES_DIR}.
See tmp/sysroots/x86_64-linux/usr/bin/scons, line 175:
175 # Look first for 'scons-__version__' in all of our preference libs,                                        
176 # then for 'scons'.                                                                                        
177 libs.extend([os.path.join(x, scons_version) for x in prefs])                                               
178 libs.extend([os.path.join(x, 'scons') for x in prefs])                                                     
179                                                                                                            
180 sys.path = libs + sys.path 

*solution
Uses create_wrapper to relocate scons-native to add `${STAGING_DIR_HOST}/${PYTHON_SITEPACKAGES_DIR}' to PYTHONPATH, so scons-native could find out the lib.