Managing Masters vs Previews in iPhoto

Tried a search of this forum but did not see this previously answered.  I have learned that iPhoto stores the original copies of imported images in a Masters folder and then when an image is edited, the resulting images are stored in a Preview folder.

When I have finished processing the images and am happy with the results, is there a way to have iPhoto delete the Master image(s) and/or promote the Preview image(s) to be the Master so that I do not have two copies of every image?

If iPhoto does not provide this capability, does Aperture?

I have started shooting in RAW and have found that my hard drive is quickly filling up.  I would like to retain the Masters of only a small subset of photos and simply keep the Previews of the remainder.  I guess one option would be to export the processed photos as JPEGs into a storage folder, then delete them (Masters and Previews) from iPhoto, then import the JPEGs back into iPhoto.  I would hope there is an easier approach than this.

Thanks in advance for your help with my question.