Does anyone know where or if there is a hack that I can use to remove this block?
Yes it can be cleared fairly easily, however it will no longer be connected to your company's BES servers, and the minute you do an Enterprise Activation to try and reattach to them, the policy will be pushed down to your BB. Used to be that this could only be done when you sync'd it via your PC, but its been doable wirelessly for a few years now.
Depending on how anal your BES admins are, they'll know that the policy has been pushed down again which could lead to a chat with your manager.
You could always try to come up with a business case to justify enabling the memory card socket for you. At least you won't have the chat this way.