The fault with that is that when you break through the gelcoat on top it will more than likely crack the gel and cause spider cracks to eminate outwards from the hole over time. Granted removing the tower is a pain but well worth doing it correctly in the long run.

If it were mine i would dril a very small pilot hole from underneath then unbolt it and just move it slightly to allow drilling. Reverse drill the hole until through the gel then forward, then countersink to prevent cracks.