Greenwich foot tunnel to Coulsden can be pretty much hill free, thusly:
Greenwich High Street, Brookmill Road, Friendly Street, Wickham Road, Crofton Park, Brockley Rise, Cranston Road, Perry Hill, Bell Green Lane, Kent House Lane, Thesiger Road, Green Lane, Croydon Road, Penge Road, Selhurst Road, Sydenham Road, Dingwall Road, George Street, High Street and then the A 235 all the way to Coulsden.
Its a route I ride regularly (to my sister) .
If you PM me an email addy, I can send you a gpx file.