I know that it's possible to copy a sketch. Too bad that only the sketch elements and some relations, but not the dimensions aren't copied.
The way to copy?
Just select the sketch you want to copy in the feature manager,then press <ctrl><c>. After this select a plane or a face you want the sketch to be copied to and select the "sketch"button. Now you press <ctrl><v>, and there it is: the copy of your sketch.
When inserting dimensions again, do this right away, and start with the element sizes, since all these are still the right size. After this, add the dimensions needed for the positioning of the sketch.