I agree with Guido. We've been certifying distances using a process that's been around for a long time. If a RD insists on specific start and finish locations that result in an odd length course, then that should be the certified course length.
I once measured a combined marathon and 1/2 marathon where the race director wanted the same start/finish for both courses. The first 1/2 was a loop on the east side of town and another 1/2 marathon distance was on the west side, which made up the distance for the marathon course. The RD did not want an out-and-back anywhere, which would have made it easy to satisfy the start/finish locations. I fixed the finish at one locaiton, and after working with the RD most of one summer, we found roads that would bring the start locations within 16 ft. of each other. I marked and certified the actual 1/2 and marathon lengths 16 ft. apart, but told the RD that if they really wanted to use the same start for both courses, they should use the longer of the two. So, the 1/2 marathon runners ran an extra 16 ft.
A couple of years later, construction forced a change to the second half (marathon course). When I adjusted the course, I added a short out and back.
Then last year, the new RD asked to have a more extensive adjustment to the marathon and insisted that there should be no out-and-back while still having the co-located starts and finishes. I declined the measuring job.