Unless you carve it out of a different strap, OR you could make a mold and mold yourself one but that's so much work and the tensile strength would be questionable. I have modified a few but just by notching ends and so forth. Nothing anywhere near 30mm though!
Rubber straps are "a good thing" until they break -- as at least 3 of mine have!
I adapted a strap to fit the Casio -- my wife is a PE teacher and is brutal on straps.
Cazalea