Slim Fast Cakes by Bonnie Gordon

After further research, I found the company that designed the Slim Fast cakes - Bonnie Gordon School of Cake Design. No the cake toppers are not for sale!

Quoting their website:

Of the many cakes Bonnie has designed for print ads, perhaps the most internationally famous are the ones she created for the Slim-Fast ad campaign.

This multi-award winning campaign with the caption "Need to lose a little weight before your wedding?" depicts bride and groom figures sinking into Bonnie's wedding cakes. The ads were so popular that they were picked up by Slim-Fast in Australia and Europe, and appeared on the cover of the December 2004 issue of Applied Arts Magazine.

http://bonniegordoncakes.com/pages/cakes/print_and_film.htm