I can't say I've done 3.5 volumes before, but I've bottled plenty of beers using my beer gun with such minimal foaming that I often "finish" the bottle with a blast of CO2 to create some foam for capping.
Cold, speed and gravity are your friends here. You mentioned chilling the bottles, but to maximize impact I'd recommend getting the beer, the line, the gun and the bottles to 34F. Also chill a pint glass and run some off into the glass for yourself. This helps equilibrate everything (including you)
Once things are cold and flowing, pay attention to keeping things cold and flowing. If you set the gun down for a few minutes to get more bottles or caps, the beer in the line will warm up. Pumping beer that's warmed in the line into a colder bottle will produce foam. Pumping cold beer into a warm bottle will produce foam. Yes, there are a lot of ways to screw this up.
Also, pay attention to the impact of gravity. Blichmann mentioned this on an old episode of Brew Strong. Just like draft serving setups, you can drop pressure either by adding more line or by adding a vertical rise. I tend to bottle on a desk with the keg sitting on the floor, so that vertical rise is probably helping me out there.
Hope this helps!