Casement window cranks
Another option: An extender that replaces the handles altogether. It's meant to be used from a distance; it's like a long tube with a crank on the end of it (I've seen maybe 3' long, to maybe 8' long, depending on your application). You replace the existing crank with what looks like a 6-sided nut--which the long handle turns. You can just get the shortest one you can find; they work like a champ!
We've had ours for several years; not sure where to find but they are out there. I'd think either of these options beats taking out that beautiful woodwork....good luck!