CO2 tank, regulator, now what?

So I have a small closet-like set up, 62 cubic feet lined with mylar. One 400 watt HPS and two 24 watt T5 CFLs for full spectrum lighting. I am three weeks into veging some white widow clones (4 in above dirt). They are in soil in 1 gallon pots. 2 Fans, a cold blowing humidifyer, and inline fan changing the air 2.5 times a min. Air goes in through a vent at bottom of door and out through the heater vent of the house out the roof. The humidity stays between 38-50% and the temp stays between 70-85 degrees f.
My question is I realised I have a 20 lb Co2 tank from a broken down kegerator, complete with regulator and a plastic tube and co2. I don'w know what else I would need, timer or such. The regulator thats on the tank works, i can feed gas through the tube and change the flow from a blast to a trickle. The meter reads in psi. I'm getting low on funds, so could I give my plants co2 using just the parts I have?

What I was thinking about doing was corking the tube, drilling tiny holes along one side toward the corked end, then hanging the tube above the plants. If I run the tank on low, it should trickle down from the holes in the tube on to the plants, I think. will this work? will it have an effect on growth? From my research, the tank and the regulator are worth around $500, so it seems like a waste just letting this resource sit unused.

No one here has been in this situation before? Anyone ever ghetto rigged a co2 system before? I really don't see why I this wouldn't work, but I just want a second opinion.

Different sources give different info, most say twice a day for a short amount of time. It seems that it changes from room to room, there are formulas and calculators I've found for how much to feed in according to cubic area, but without a gauge, I cant be exact. If anyone has any knowledge to help us out it would be great. I'm probably gonna end up ghetto rigging unless someone has a good reason not to, as I keep seeing this ten lbs of co2 sitting here going to waste. I guess the main thing I want to know is do I keep ventilating during the fifteen min? how about air circulation in the room(fans, humidifyer, etc)?

so i know its been almost a year, but i was looking for this information as well and didnt find anything right away.

but to the people doing the same thing i just did who are reading this...

i found this pdf file that will surely be helpful
http://www.hydroponics.net/documents-hf/16563_COSYSinstruc2.08.pdf

and also, this calculator.
http://www.hydroponics.net/learn/co2_calculator.asp