You should know what your desired level of CO2 is for this beer which ends at 1.008 and is racked at 1.011. These are 2.75 and 2 degrees Plato respectively. You need to convert volume of CO2 to grams of CO2 per liter.
volumes of C02/(0.506 volumes/gram of CO2/liter)=grams of C02/liter
2.2 liters C02/liter beer/(.506liters CO2/gram of CO2/liter beer)=4.34 g of CO2
or more simply 2.2/.506=4.34g of CO2. All the liters cancel out in the equation leaving you with grams.
If you know the desired grams of CO2/liter, take this and divide by 0.46 to obtain the required fermentable extract. For instance, if you want 5.5g of C02/liter then take 5.0g/0.46=10.8g now take this and convert to Plato. 10.8g/1000g in one liter=1.19Plato. Now add this back to your final apparent extract of 2Plato(1.008). So 1.09+2Plato=3.09Plato. This shows you that your never going to hit your target desired amount of CO2(5.0g) because you are essentially bunging the vessel and capturing CO2 too late in the game. You are bunging or racking the beer at 1.011 or 2.75 Plato and finishing at 2 Plato. You are going to have to rack over the beer at 3.1Plato in order to hit 5.0g CO2. 3.1Plato is 1.012. You are very close but not quite there if you are trying to achieve 5gof C02/liter. But this is essentially your route to an answer. Just know your desired amount of grams of CO2 and then work from there!
I hope this makes sense.