gistfile1.py

import os
import sys
import glob
import expressions

from qgis.core import QgsApplication

def load_user_expressions(path):
    """
    Load all user expressions from the given paths
    """
    #Loop all py files and import them
    modules = glob.glob(path + "/*.py")
    names = [os.path.basename(f)[:-3] for f in modules]
    for name in names:
        if name == "__init__":
            continue
        # As user expression functions should be registed with qgsfunction
        # just importing the file is enough to get it to load the functions into QGIS
        __import__("expressions.{0}".format(name), locals(), globals())


userpythonhome = os.path.join(QgsApplication.qgisSettingsDirPath(), "python")
expressionspath = os.path.join(userpythonhome, "expressions")

# TODO Look for the startup.py and execfile it

expressions.load = load_user_expressions
expressions.load(expressionspath)

gistfile2.py

Python Console 
Use iface to access QGIS API interface or Type help(iface) for more info
>>qgis.user
<module 'qgis.user' from '/home/nathan/dev/qgis/build/output/python/qgis/user.py'>
>>qgis.user.expressions
<module 'expressions' from '/home/nathan/.qgis2/python/expressions/__init__.pyc'>
>>qgis.user.expressions.load
<function load_user_expressions at 0x7f7163cde8c0>
>>dir(qgis.user.expressions)
['MyFunctions', '__builtins__', '__doc__', '__file__', '__name__', '__package__', '__path__', 'load', 'scratch']