Nodal analysis - what to do when a supernode spans entire circuit
You don't need to do anything weird to handle the lower left branches. Treat the dependent voltage source the same as you would an independent source. If \$V_1\$ is the node between the 10 and 20 ohm resistors, \$V_2\$ is the node between the 40 ohm resistor and the 120 V source, and \$V_3\$ is the node between the dependent current source and the 80 ohm resistor:

$$\frac{V_1 - 100\ \mathrm V}{10\ \Omega} + \frac{V_1 - 4V_O}{20\ \Omega} + \frac{V_1 - V_2}{40\ \Omega} = 0$$

You've introduced a new variable (\$V_O\$), so you need another equation to solve the circuit. This equation should define \$V_O\$ in terms of the node voltages. In this case, \$V_O\$ is simply equal to one of the node voltages:

$$V_O = V_3$$

You can use a similar technique for the dependent current source.