Open a different image than the thumbnail

Hi! I'm trying to see if this sort of thing would be at all possible. I'm using Brine template Maple, 7.0 and a gallery grid block.

I know that what I'm trying to do will deem gallery useless and I will have to do each image separately as a block but... worth a try. So I have a hero image that focuses on a product smack bang in the middle as I'd like that as the thumbnail- but then I'd like to be able to click it to open in a lightbox with dark overlay to show (in essence, a completely different photo) a line-up of the whole range/flavour SKUs. 

Any help would be much appreciated!