Soaking a "ball" cake

Hello,

I am no expert. I just enjoy baking for the family and some friends. I am baking (or attempting to) a bowling ball cake for granddaughter. I used a dense buttery recipe and was wondering if I can soak it with a syrup. I normally make one with water, sugar, rum and vanilla. If possible and wont ruin it, I am guessing both halves are soaked separately and then are put together with a layer of buttercream? I would appreciate any help you can give me. The birthday party is this coming Saturday, 7/18/15.

Thank you!!!!