This won't change the sketch orientation, but an easy view orientation that is built into to SolidWorks lets you pick a temporary top plane.
First you click (LMB) the plane you would like to be normal to. Next you hold control and click (Ctrl+LMB) the plane you would like to be parallel and closest to the top of your screen. When you then hit the normal to button, you will be normal to the first selected plane with the second selected plane on top. Be careful if you do this with a left or right plane because the sketch will then see horizontal and vertical based on the origin and not on your current view.
You're correct about the easy view orientation. I've tried that but then horizontal lines are treated as vertical and vice versa.
When you create the plane and click on the plane you want it to be normal to, on the left hand menu click parallel rather than Perpendicular. If the plane is of the front, right or top variety you can click on them in the flyout features menu and make them offset?
Any of this help?
After you create the sketch, you can change the orentation,
Edit the sketch, go to tools, sketch tools, and Modify,
A black L shape Origin will show up,,
look on SW help for modify sketch it will show you the options to mirror, rotate....