Easiest way to do this is to build a "spunding valve". Basically a valve with a pressure gauge on it. Keep an eye on the gauge, and multiple times per day open the valve to release pressure. If it's at room temp, aim for around 25-30 PSI in the keg, and this should carbonate you up.
You could try a calculation based on sugar being consumed and CO2 being produced, but it'd be hokey at best, and I'm not adventurous enough to try it. If you want to try though, you need to determine how much sugar is left at any time in the beer. Remember that your expected FG of 1.011 has a certain amount of ethanol in it, which has a much lower density than water, so you have to account for three variables, (water, sugar, alcohol), in determining how much sugar is left. Once you have that, you could determine how much CO2 is produced (STP values) based on the chemical equation for sugar -> ethanol, (wikipedia that). Then, knowing how much CO2 you need, (2.4 volumes, for example, would be 2.4*5 = 12 gallons CO2 at STP in a 5 gallon batch), you would know when to seal up the keg.
Spunding valve is a bit more foolproof though. I suppose you could also get a secondary regulator and hook that up to the gas QD and set it at 28 PSI too.
