If I'm gonna laugh, it's because you used a "scaffolding calculator".
Are you sure it's that high? I've built some seriously tall two-story homes that aren't more than about 30-35'. Plus, you don't need 40' of scaffolding to reach 40'. The painter can reach 6-8' him/herself.
Do anything you can short of damaging the home. Run a rope through a window to the doorknob.
If you're on stable ground, it's just a precaution. You could run rope along the house, perpendicular to the scaffolding, to some heavy stakes.