EKM Email Marketing - Segmenting signups at Checkout

'I would like to be able to have customers signup to different groups at checkout depending upon which items they purchase. For example, if a customer bought Nikon equipment from us it would be great if the email signup option that they were given was to a specific group for Nikon equipment. Same for those buying Canon and other brands.
The benefit of this is that we could then send more targeted emails to the customers depending upon what group they are in. It would be great if we could create contact groups and then assign email subscribers to those groups automatically depending upon the items that they purchase.' - David