Okay so i have been giving this some thought. Without the Z axis, doing this with Physics is gonna be really difficult. So I'm thinking of approaching this with Animations and variables. Just thinking out loud here so let me know if this seems feasible.
Set up a variable for the ball speed.
Variable - Ball Speed = Slow, Medium, Fast
Set up three hit markers in front of the pins, they will be a single sprite image instead of each single pin.
Targets - T1, T2, T3
First Throw
Ball on collision with T1 and Anim 1
Speed = S - Play Anim 2
Speed = m - Play Anim 3 = Strike
Speed = f - Play Anim 4
Ball on collision with T2 and Anim 1
Speed = S - Play Anim 5
Speed = m - Play Anim 6
Speed = f - Play Anim 7 = Strike
Ball on collision with T3 and Anim 1
Speed = S - Play Anim 5 -Mirrored
Speed = m - Play Anim 6 -Mirrored
Speed = f - Play Anim 7 -Mirrored = Strike
Firs throw we have 6 unique Anims for them hitting the pins.
T3 can just be mirrored over from T2 as it's the same thing just on the opposite side.
Second Throw
Ball on collision with T1 and Anim 2
Speed = S - Play Anim 8
Speed = m - Play Anim 9
Speed = f - Play Anim 10
No Set for Anim 3 as that resulted in a strike.
Ball on collision with T1 and Anim 4
Speed = S - Play Anim 11
Speed = m - Play Anim 12
Speed = f - Play Anim 13
Ball on collision with T2 and Anim 5
Speed = S - Play Anim 14
Speed = m - Play Anim 15
Speed = f - Play Anim 16
Ball on collision with T2 and Anim 6
Speed = S - Play Anim 17
Speed = m - Play Anim 18
Speed = f - Play Anim 19
No set for anim 7 as that resulted in a strike
Ball on collision with T3 and Anim 5 -Mirrored
Speed = S - Play Anim 11 -mirrored
Speed = m - Play Anim 12 -mirrored
Speed = f - Play Anim 13 -mirrored
Ball on collision with T3 and Anim 6 -Mirrored
Speed = S - Play Anim 14 -mirrored
Speed = m - Play Anim 15 -mirrored
Speed = f - Play Anim 16 -mirrored
In total we are looking at 18 different possible animations for when the pins are hit. And 1 animation for when the ball hits the gutter lane. Gutter lane anim can be mirrored as well for the opposite side. Looking at 19 animations possible.
To me this seems the most efficient way to approach it, but maybe someone has a better idea.