Randomly discovered FEs concern about Google Walking Mode, which has vexed me too. I frequently do a clockwise Deeside Loop from Banchory, my fave summer ride, as a 200k DIY except that Google insists on routing Kirriemuir-Banchory past Dalnaglar Castle and over a deep burn [Shee Water], where there is no sign of any past or present bridge or ford [I have been there and looked]. So I can put in an extra point on a route that is otherwise elegant in its minimalism, with 3 controls plus start/finish. Yes I know the advice is every 50k, but...
The Deeside Loop is such a well-known route that the regional DIY org will almost certainly not raise an eyebrow at an entry with a route-shaping point that forces the route on-road.
I'd not bother to add the point as an actual control.
Just add it to the route on Google Maps to force the route, and when you submit the route to the org, either add a note about the route shaping point, or don't bother.
In this specific case, I'd not bother.