To make double-layer copies without "shrinkage" you will need a burner that writes double layers and use double-layer media.
Another way to avoid shrinkage is to stay out of cold swimming pools.
By followng all kinds of links starting at "DVD Decoder" I found something called DVD Rebuilder -- it seems to be able to handle multi-layer DVDs BUT it has been running on one of my short DVDs for the last 2 hours -- it is 80% complete but it seems to be writing work files named ".M2V" so I'll ping back if it succeeds.