No, but holding CTRL anchors at the bottoms center.
There have been times (complex animation) when I absolutely needed to rotate
at a corner from within PowerPoint. I traced the outer shape of the object
(clipart) using SnapToShape and the Rectangle tool. Then I moved the drawn
shape into an upper diagonal position of the clipart and made the box
no-fill/no-line. I grouped the two. When I rotated now, it anchored from the
corner of the clipart.
