After much searching (on these forums and the internet) I was unable to come up with much information on the 'ambient light sensor'. This is the little sensor on the passenger side of the dash, right next to the speaker, that detects the light outside and tells the lights when to pop up.
My problem with this system was that I found it being too sensitive; drive under a bridge - lights pop up, through some heavily treed areas - lights pop up.

So I finally decided just to dive into it.

I have also attached a wiring diagram showing the photoresistor
I should also mention that I cut out the connector and worked on a bench BEFORE I realised that the sensor comes apart from the connector.

Note: This is something I have done and has worked for me, but I'm not going to be held responsible for anything you do to your own car!

You will need a ratchet and 7mm socket to get the dash pad off and out of the way, a multimeter, and some basic know-how.

First I took off the dash and removed the sensor - the sensor is held in by a twist-lock connector just like the PC194 bulbs on the instrument cluster and very similar to the connectors on marker lights etc. So just twist, pull it out and get the dash out of the way. (see 1st pic)

The sensor itself comes out from the connector just like a 194 bulb; so just pull the little blue piece and it should pop right out. (see 2nd pic)

Time to bust out the multimeter - specifically the ohmmeter. You're going to want to measure the resistance across that little sensor you just pulled out.
It's actually a photo-resistor, meaning it will have a different resistance in the light from when it's in the dark. The resistance you will want is in the light, we're going to trick the car into thinking it's always light outside.

My resistance number in the light was 1000 ohms in the light and open circuit in darkness. EVEN THOUGH IT SHOULD BE, PLEASE DO NOT ASSUME YOURS WILL BE THE SAME!

Now time for some math so we can get a resistor that will work. The DRL module sends out a 5V reference signal, through the photoresistor and back to the module; this tells the computer if it's light or dark, in turn telling the headlights to be on or off.

Since E(voltage)= I(current) x R(resistance) and we know E(5V) and R(1000ohms)
I=E/R ----> 5V/1000ohms = I = 0.005Amps

Since resistors are rated for Watts and not amps we need another formula

P(wattage)=I(current) x E(voltage)

0.005A x 5V = P = 0.025W

This is how much power will be flowing through the circuit.

So I went down to my local electronics store and found a 1000ohm resistor good for 1/8 Watt (0.125Watt) which is much more than it will need to handle.

Just bend the tabs on the photoresistor and it should slide right out of the blue base it's in.
Slide in your 1000ohm resistor and bend the tabs the way they were and trim any excess length.

The blue base will pop right back into the connector, the connector will pop right back into the dash.... and voila, now you control your headlights