If you use the shake method you should be able to have it carbed up. Make sure it's cold and use the shake method periodically to get it to the desired level. Usually this is done at a higher pressure, say 25-30 psi, but I'm not sure if the fact it's been sitting on the gas for 4 days already will make a difference or not. I've never done that myself.
Also keep in mind that by forcing the CO2 like this you're going to get a lot more of a carbonic bite type flavor, which can be quite a distraction. IMO it would be a shame to rush a Pliny clone and have an end product that isn't as good as it could be.