Jury-rigging a 5

no sewing tonight. (other than maybe a quiver.... we'll see how my indoor (as opposed to garage) sewing machine likes sewing vinyl... it might happen tomorrow instead)
ANYWAY, tonight is all about the cake.
(two little cakes, 1 for each child tonight. btw, the pans are not the same size, but each have the same amount of cake batter.)
 Last year, I discovered this GORGEOUS book, with this amazing cake. and my boy wanted a "farm" themed party, so we bought the book, and I made a cake shaped like a 4, we decorated it, it was cute. easy. 
this year, he's turning 5. 5s are curvy. (see the curve?)
this book says you need a ring cake tin. I'm not buying a ring cake tin (I admit, I looked for one, but neither Jo-an's, nor Target had one, and that was as much looking as I was willing to do).  Nor am I buying a cake tin shaped like a 5. 
Ergo:
a round cake tin with a parchment-paper wrapped, water-filled jam jar in the middle.