Shifters/brakes won't fit on bullhorn bars
I would advise against the grinding idea.  You might be okay if there's enough meat left on the ring, but these are part of your braking system, you really don't want that to fail.  Imagine an emergency situation, or even an intersection at the bottom of a big hill.  You squeeze the levers hard and the mounting rings break, your brake cables go slack and you can't slow down or stop.  Even assuming only one ring were to break, you'd have maybe half of your stopping ability remaining which could easily lead to injury (or worse).  The breaking of the ring could also startle you enough that you lose your grip on the handle bars.  Not worth it.