I inserted 2 plastic spirals into my dip tube on my kegs and this worked unbelievably. I would maybe try 3 in your case and go with a 3-5 foot line. I used two in a raspberry fruit ale, I was aiming for 2.1 volumes I have a 60" line @ 12.5 PSI. It pours slowly but the Co2 is spot on.
See this...