To further elaborate on the tumble notion (warning, horribad programmer art):
Attachment 1350675097
Figure a rotated Y axis as opposed to the flat one we've got now when we've a target, possibly followed by a scripted attack after the tumble animation, either with, or without a +W modifier. Distance limited either by distance to target + weapon range (so you can pop behind them if you've got that tumble through target mod) or your tumble skill, in order to encourage folks to spend more than the minimum amount required by their armor/shield values (which also somewhat might encourage taking rogue levels further, since that gives folks that many more skill-points to play with to support it).