Aligning midpoints to grid?

Is there any way to get Omnigraffle 6.1.1 to snap all the midpoints of a line onto the grid? When I create a midpoint by double clicking on the line, the midpoint is almost always not on the grid, forcing me to manually get it onto the grid via option-(up,down,left,right). Selecting the midpoint and hitting Command-Option-[ (“Align objects to grid”) isn’t effective (that simply places the top/left corner of the line object onto the grid, which does nothing for off-the-grid midpoints), and “Snap to grid” doesn’t seem to apply to midpoint creation. I’m working on a map with precise curved line segments, and dealing with all these tiny off-by-1/1000ths is becoming a major pain!

During my two-week trial, I was able to fix this by just hand-snapping the x,y coordinates of the midpoints (I’m working on a 10mm grid, so this is really easy), but I’m pretty bummed to discover this is actually a “Pro” feature—given that there doesn’t seem to be a way to create midpoints on the grid, this turns what should be a very simple thing into a major pain!