Add parameter for custom launch function to KernelManager.start_kernel.

IPython/zmq/kernelmanager.py

@@ -771,6 +771,11 b' class KernelManager(HasTraits):'
         ipython : bool, optional (default True)
              Whether to use an IPython kernel instead of a plain Python kernel.
 
+        launcher : callable, optional (default None)
+             A custom function for launching the kernel process (generally a
+             wrapper around ``entry_point.base_launch_kernel``). In most cases,
+             it should not be necessary to use this parameter.
+
         **kw : optional
              See respective options for IPython and Python kernels.
         """
@@ -785,6 +790,8 b' class KernelManager(HasTraits):'
                                )
                     
         self._launch_args = kw.copy()
+        launch_kernel = kw.pop('launcher', None)
+        if launch_kernel is None:
         if kw.pop('ipython', True):
             from ipkernel import launch_kernel
         else: