Strict RAW interpretation of the rules does allow for railroading as described. It's not something I would ever implement myself. It isn't an issue of movement, but rather an issue of coming within 1" of an enemy unit (outside of CC or as part of a charging move). An ordinary unit could easily move forward and pivot as you described, but a model with Random Movement cannot... they always move in a straight line. An HPA would typically declare a direction of movement, pivot and move 3d6" in that direction... if it comes into contact with an enemy it counts as charging (which allows it to charge units outside of its line of sight and front arc). However, if there is a model an inch away from it on its flank, then even the smallest amount of pivoting would bring the corner of its base inside of 1", which is disallowed by the rules. I view it to be a dirty tactic and gamey. It may be allowed by RAW, but as a subscriber to RAI, I would never play it that way. Many tournaments and gaming groups adopted something called a "virtual pivot" that allows for a model to break the 1" move during a pivot, thereby preventing this railroading tactic.