You could define a new reference plane using 3 vertex in the model if available then create a sketch on the plane placing a point you would like the axis to start normal to the plane. If there are no appropriate vertex's then try inserting a 3D sketch to place 3 points with which to define the plane.
I read this trick here before for creating a plane perpendicular to the camera view:
1. Angle the camera the way you want.
2. Start a 3D sketch and draw 3 points out in space off the part.
3. Drag all 3 points to the origin.
4. Delete all of the relations on the points.
5. Drag the points back out into space off the part. This drag will move them out in a direction perpendicular to the camera view.
6. Exit the sketch and make a new plane from those 3 points.
Now you can sketch on that plane or use it to define more planes/axes.
I like that one going to note it down for the future.