If you drop the oven temp a little the cake won't rise as much either, so you won't have such a bog issue to flatten the top off after it is coked, regarless of how thin you bake the cake to begin with.

Try a sponge recipe you might be able to get a thinner better result than a butter cake. That way you can use a slice tin of some description, as that is as shallow, if not more so, than a victoria sandwich tin.

HTH Cant wait to see the pics when it is finished, sounds awesome!