Aaaah I see, I thought you wanted to draw it yourself and you wanted the auto route feature switched off completely.
I think the answer to your question is therefore a combination of manual and automated options, youcan use the 'prefer minor roads' option from the route preferences options (edit -> preferences -> routing -> road selection) in combination with custom avoidance areas (and just set the avoidance area as a rectangle covering the adjacent highway or problematic area)
but to be honest, if I was doing the same task, I'd start by entering the start and end point precisely, then let MapSource draw a route between the two points and then start correcting it by selecting the route at intermediate incorrect points and dragging the route back onto the correct road until you get a result you're happy with, this is IMO the only way you'll get a good quality result.
If you see what I mean:
(for more explanation, see page 15 of this doc
http://www.bestbikingroads.com/usefu..._Tutorial1.pdf
)
Does that help?
David