Can't seem to find an answer to this when I search. What's the best way to stack dummies with real cake?

Was thinking of doing an extended tier or double barrel with a 3 inch dummy and a 3 inch real cake. This would be on top of another larger dummy. What would be the best way to stack this? 

Should I pu the real cake on top and dowel through to the dummy with a thin board in-between the 2?

When I do mine I put a little buttercream between the tiers and that seems to hold.