I had a 11x15 cake to do for my granddaughter's BD this past weekend and I did not want the bulges that I sometimes get between the layers. I tried a variation of this method, and mixed Marshmallow Fluff with my buttercream and after piping the dam and laying the top cake on I turned the cake pan over (11x15) and put my heavy plastic flour container on it and let it set for a couple of hours. The weight was evenly distributed across the cake and the flour had to weigh about 15 pounds
. It worked perfectly but, I do have some tile left from the house being built and I am going to try this.
As far as filling coming out when you try to compress the layers, do not spread the filling to the edges of the dam and do not overload the filling between the layers. The weight of the tile will spread it out nicely for you. Another idea (from someone on CC, don't remember who) is to use cake with your icing and make a dam with that mixture so there is cake in every bite.