I wouldn't think golden would have many flat and rolling rides. Wonder why?
The platte trail is fairly flat but has underpasses and places you would need to get out of the aero bars.
Maybe somewhere closer to Kansas?

The only ride I have ridden lately that would fit the bill would be taking the I-25 frontage road from 160th ave to johnstown. Boring! Still it is flat / rolling. I sat in my drops for the 70 mile ride to Greeley and averaged 19 mph.
One could always find a place like Washington park and do laps.