Is there a similarly direct way to have images rejoin their original projects (I doubt it)?
No, the "Put back" from the system trash is not availabe for Aperture library items. It would not suffice to write these files back to their folders in the library, they need to be properly imported and indexed in the databases inside the library package.
If not, how do I get them back into Aperture which too much ado?
The trash will contain a folder "Aperture". Drag this folder to the Desktop and use the "Import" panel in Aperture to reimport the images inside. If your images came from different projects, the "Aperture" folder may have subfolders named like the projects that the images came from. Then import these folders one by one back into Aperture, sort your projects by name in "Projects" view and join the reimported projects with the original original projects by dragging the reimported projects onto the original projects. It will help to flag or color label the reimported images, while they are still visible in the "Last Import" album. This way you will be able to search for them.
I noticed however, that Aperture will not always separate the deleted items into folders, when they are in the Trash. Then you will have to find other ways to recognize the original projects, based on the dates or filenames.