Discount codes applicable to parameters

Hi,

During a tech support ticket it was suggested I place the following product feature recommendation here:

Allow option for discount codes to be applicable to pricing relative to specific parameters in a booking rather than to the entire total. For instance, we may have three parameters: Adult, Child, Senior and a booking that has one of each. However, we want a discount code (e.g., Senior30) to only discount the senior rate of the invoice by 30%.

Thanks.