The coast ride is pretty flat, you have to head east for any real elevation changes, you might be able to make it down to Rancho Santa Fe or Lake Hodges but you will need about an hour and a half each way. Maybe ride down and explore then get picked up at a main road before heading down to Del Mar for lunch. Heres a few other ideas http://www.bikely.com/listpaths/country/254/region/126/city/7126