Hi Colm – this is possible with the new Scripting Module which we’ve just released (in update 1052).
We’re working on a load of examples which will be posted to the forum to assist users with writing their own scripts, but in the meantime, please feel free to contact our helpdesk to get some assistance in writing a script to calculate BMI.
(By the way – I should add that you will probably need to purchase the Scripting Module if you haven’t already done so!).