The Math Olympiad problems do not inherently require a lot of writing, they are thinking problems with a single numeric answer. My borderline-dysgraphic son has more trouble with being willing to write down intermediate steps and rushing through problems with the wrong assumption than anything else.
His outside of school math club talks through the problems and solutions with minor notes on a white board. If discussions aren't central to your school's club, then encouraging that is probably of benefit to everyone.
