Lyman,
Below is how our manual suggest you deal with this situation.
APPENDIX A - Supplementary Tips
Dealing with Obstacles
When measuring the course, you may encounter an obstacle, such as a parked car, that will not be present on race day. One way to deal with this problem is as follows:
a.stop your bicycle just before the obstacle
b.freeze your front wheel with your hand or the brake
c.very carefully move the bicycle perpendicular to the route being measured until you are clear of the obstacle
d.release the wheel and proceed until past the obstacle
e.reverse the process with the wheel frozen to return to the shortest possible route
Use this procedure sparingly and report each instance in your application for certification. If you have to do this more than a few times on the course, try again on another day when most of the obstacles are gone.