Implement a new option on roadsigns/roads that appears when you are lifting an object that will give you the option to send it along the road system. Might crowd up the flower menu too much however, so just tacking on a "Send Item Along ..." option may not be the best approach. Maybe shift right clicking it could bring up a submenu with more intricate options like sending along objects/animals.
The item will look within a small radius around the end of the roadsign for a place to be dropped, and return an error message if there isn't room. The idea here is so we don't have to travel to the end of the road every time to set down a barrel of water or a boulder for example.