The correct solution to this problem is to learn to use the rudder, but
there is one airframe modification that could be worthwhile. The strongest
effect causing your plane to veer left is the 'spiral slipstream'. The air
blown back by the prop has strong swirl. When this swirling flow strikes
the vertical stabilizer, it pushes it right, which steers the plane to the
left. This effect is generally stronger than P-effect in any case, and in
this case we know it is, since the tail on a tail-dragger picks up, making
the angle of attack of the plane small. One way to minimize the steering
effect of the swirling flow is to add some fin area below the center line
of the plane, so that some of the swirling flow hits it from the right. You
could remove some area from the top of the fin as well. A fin with the
same amount of area above and below the center line will almost eliminate
this swirl-induced steering. To reduce the strength of the swirl, you could
also consider a prop with less pitch.

Because the fin is more effective at stabilizing the plane at high speed,
is also helps to throttle up gradually, as the plane accelerates. This way,
the 'weather vane' effect of the fin increases as the swirl increases, so
you don't need to use as much rudder. A typical full throttle takeoff gives
you the maximum amount of swirl in the prop wash right at the beginning,
when the fin doesn't help you out at all.

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