If you don't want to relocate the pipes, and it's unlikely you'll be able to insulate them, the only other choice is to pick up a hot water recirculation system. Lots of companies make them. Since you don't have a dedicated return line, the retrofit units utilize the cold line as the return, so that water line will get somewhat warm (there's a thermostatically controlled valve or control to prevent it from getting the full temp of the hot line. I have one made by RedyTemp, but there are lots of others that would work, and work well. if you search the forum on recirculation, you'll find lots of info on brands and issues. You can set the thing up on a timer, a demand switch (that only runs when you press the button for a short time), an occupancy sensor, or constantly.