You can fill the core with cake mix and use it as a plug to fill the hollow area. Be sure to coat the inside of the core the same as you do your cake pan and it should come out easy. Put a little BC around it once it's cool and place it in the hole. HTH
i also fill the heating core when i use it and plug the hole with the cake from the core. ALSO, i have used a flower nail for a heating core... works fine.
flip it upside down... pointy end up..... let the flat part rest on the bottom of the pan......
hmm.... ok... so now i'm remembering you have the stand up tree pan? hmmm.....do you have a wonder mold? it comes with a heating ROD......
i think i'm going to babble on any second now..... but, do you HAVE to use a heating core? 
and now i just read your original post and you asked if you had to use a heating core!!!! 
i dont think you need to. its only one cake mix.... and i dont think the directions call for it..... if they did, the pan probably would have come with a heating rod like the wonder mold does.......
it does come with a core. if you use a flower nail instear of the core just let it bake untill it's 1/2 done then insedt the nail the batter should be thickened up enough to hold the nail just place it carefully. This should work i use it for my big pyrex i use a flower nail in top and bottom.
Quote by @%username% on %date%
%body%