In the Save As dialog in Automator, save your project as an Application. Back in the Finder, Control-click on the newly-creatd application and pick Show Package Contents from the pop-up menu. Open the Contents folder, and inside there is a file called document.wflow. Drag this file to your desired destination and delete the original application. Now you have a small file -- like a workflow -- but one that can be run with a double-click, like an application.
[robg adds: I tried this, and it worked as described. My simple two-step workflow was 384KB when saved as an application, but only 12KB when I extracted the workflow. There are probably a few downsides to this approach, though I'm not sure what they might be -- so comment away!]

