To get a snaproll, you'll need a lot more Rudder than anything else. Most trainers have a very large fixed vertical stab and a small rudder, which makes them hard to get into snaproll or spin. Moving the CG back is also critical, as is enough elevator throw. But frankly, even my juiced up trainers never really snaprolled very well even if they did great spins. Part of the issue is the very low wingloading and the shape of the airfoil and straight wings all combine to make the plane resist stalling, and when a stall does develop it's usually at the root of the wings, which makes for a slow roll and a quick, automatic recovery.

Depending on what you get once you max out the rudder and elevator travel and seal everything up, and move the CG way way back, you might consider replacing the rudder with a bigger one.