Once you understand which area is a blocker (most of the time it's a single point - if not - you might be going against traffic), you set points around it, set routing mode to "draw lines" and then just drag the route between points - should be a straight line.
Problem is it's about 60% of the climb up the Agnel (RWGPS confirm it's due to the road being closed as it's winter). Anyway, as I said, Strava doesn't care so I did it in Strava and will tweak it in RWGPS later.
RWGPS has line drawing mode as well.
Once you understand which area is a blocker (most of the time it's a single point - if not - you might be going against traffic), you set points around it, set routing mode to "draw lines" and then just drag the route between points - should be a straight line.