Older transformer like the one pictured above were designed to work with a multi-socket adapter (#6099, shown separately below).
|#6099 multi-socket adapter, top|
|#6099 multi-socket adapter, bottom|
If you have an older transformer without a multi-socket adapter, you can do as shown in the March 2008 insert to the Lundby Letter: Cut the plug of a Lundby extension cord in half and insert the separated prongs directly into the grommets on the transformer (anchor them using Sticky Tack or a similar product). Then plug one end of the bridging cord into the extension cord and the other into the house. Follow the same technique for an extension floor.
Many thanks to We Love Lundby Club member Patricia Harrington, author of the Lundby Letter inserts mentioned above, for her expert guidance and for the transformer instructions.