В общем решил эту проблему, кому интересно код
Код
foreach (Transform transform in Selection.transforms)
{
RectTransform t = transform as RectTransform;
RectTransform pt = Selection.activeTransform.parent as RectTransform;
if (t == null || pt == null) return;
Vector2 newAnchorsMin = new Vector2(t.anchorMin.x + t.offsetMin.x / pt.rect.width,
t.anchorMin.y + t.offsetMin.y / pt.rect.height);
Vector2 newAnchorsMax = new Vector2(t.anchorMax.x + t.offsetMax.x / pt.rect.width,
t.anchorMax.y + t.offsetMax.y / pt.rect.height);
t.anchorMin = newAnchorsMin;
t.anchorMax = newAnchorsMax;
t.offsetMin = t.offsetMax = new Vector2(0, 0);
}