I'm an active course measurer for road races and peruse the RRTC bulletin board regularly. (http://measure.infopop.cc/eve/ubb.x if you are interested.) Despite what I've read here a couple times and in a few other places connected with XC season, I do not believe the RRTC has approved a method for certifying XC courses as of yet. I have seen course maps made to the same standards you see on the USATF road races certified courses list, for example Fairmount Park in Philadelphia, but I have not actually seen any certification paperwork for those courses. You can search for courses here:
. If you find any XC courses I'd love to take a look at the maps.
Given the requirements for measurement as well as the calibration needed, I don't see how one could measure a course for certification using the traditional Jones Counter on a bicycle method. The only way I could see measuring an XC course for certification would be using a steel tape, which would be hugely onerous for any XC course. And as noted above, around corners would be an issue with most tapes.
And then you have the issue of setting up an XC course to the measured standards. The map I saw for Fairmount Park went into great detail for some areas, which made it seem do-able, but for most courses I don't see that as a possibility without establishing permanent markers/posts.
To me, wheel out your XC course, get it as close as you reasonably can, then go race it. If it's 5000m or 4960 or 5050 who cares? As a coach it's always nice to know if a course was a little short or a little long, but unless we're talking 7500m for an "8k XC" course or hundreds of meters long I've never felt the need to know exactly.