Why dont you just wrap your pants around your leg and use a rubber band or a commercially made pant holder. They cost about $1.50.
Just yesterday evening I rode 10 miles in nice slacks and a shirt and tie with no problems. I realize that some people can get chain grease on their leg no matter what they do. I have a friend who can ride 5 miles and will have grease from her toes to her face. Go figure.