Example of using an existing PyQt4 class layout and adding Maya UI elements into the child layouts.

pyqt_hypergraph.py

import maya.cmds as cmds
import maya.OpenMayaUI as mui

from PyQt4 import QtCore, QtGui
import sip


class Window(QtGui.QWidget):
    """
    An arbitrary layout representing something
    that could have been created using Qt Designer.
    Has main layout, and then child widgets with their
    own layouts.
    Set object names, so that Maya will use them in the
    path structure.
    """
    def __init__(self, parent=None):
        super(Window, self).__init__(parent)
        self.setObjectName("MyWindow")
        
        self.layout = QtGui.QVBoxLayout(self)
        self.layout.setObjectName("mainLayout")
        
        self.hgParent = QtGui.QWidget()
        self.hgParent.setObjectName("hgParent")
        self.hgParentLayout = QtGui.QVBoxLayout(self.hgParent)
        self.hgParentLayout.setObjectName("hgParentLayout")
        self.layout.addWidget(self.hgParent)
        
win = Window()
win.show()
win.raise_()
win.resize(600,400)

# Get a pointer to the QObject (the layout)
layout_pointer = long(sip.unwrapinstance(win.hgParentLayout))
# Get the Maya path to the layout:  
# "MyWindow|mainLayout|hgParentLayout"
path = mui.MQtUtil.fullName(layout_pointer)
# Just set it as the current parent UI
cmds.setParent(path)
# Create a hyper graph panel, which will end up in the layout
panel = cmds.hyperPanel()

# Verify the location of the new hypergraph
print win.hgParentLayout.itemAt(0).widget().objectName()
# PyQt4.QtCore.QString(u'hyperPanel1') #