I puchased an nice bundt pan for the show to use as set dressing. As a bonus I was able to use the cheap plastic liner for this project. We filled the liner with great-stuff and let it expand overnight. It expanded to overfill the liner, but the foam at the very bottom of the mold (the top of the cake) hadn't cured because no air could get to it.
We removed the cake from the liner, cut off the over-expanded bottom of the cake so it would sit flat, and allowed the top to finish curing. Since it was no longer curing inside a mold the top became a bit more uneven and bubbly, which didn't particularly matter for this project, but is good to remember for next time.
I sprayed the cake with some glossy wood tone for color.