Even if you did manage to bore out those thin plastic grips to the 24mm road diameter without splitting through them. how do you expect to slip them past the curved drop section of the bars to reach the top?

i don't see it happening

once i did make myself some custom grips... I took cork sheeting and rolled a cork tube around bars, glue into shape. then kept adding more curved layers of cork to sculpt a form... finalize with shellac
You might try something like that... but it'll be permanent...


Or you can just do the sensible thing and switch to trekking handlebars. Remount your road levers on the curved fronts, put the ergon grips on the flat rear sections.