I haven't figured out a good solution to this kind of problem, and I don't think anyone else has, either.

The problem is that all the obvious routes you'd use by car are not very good bike routes, and vice versa. So if you start looking at charity rides or randonneuring routes, they'll route you over all these little county roads that you wouldn't ever think to go down otherwise. (And beware the randonneuring routes, they may route you over every hill in the country!)

You might try using Google Street View on those routes, may tell you a bit about them, at least in towns.

You might check in the Texas subforum, also.