i found a cheaper solution: I installed X11, downloaded FontForge, and figured out how to copy Ezra's Kamatz Katan glyph into SBL Hebrew. It doesn't line up 100% perfectly but it's pretty darn close.
In Fontforge, you can correct alignment problems with anchors. Look at Ezra SIL to see what I mean. Open a character in the outline editor. You will see all sorts of anchor points at the bottom of every letter. Those correspond to specific 0-width characters, which are tagged to use one of those anchors. If you can find an anchor that corresponds to the width of your new diacritical marks, you can just switch your new characters to that anchor point, and everything will line up properly.
Worst case, you would have to create a new anchor, and individually position it for every character, then assign your new marks to that anchor. A tedious process to say the least.
My hats off to the creators of Ezra SIL for such a meticulous job.