When I order Domino's online, I would always get the surpreme traditional pizza, remove all the toppings that I don't want and then add on the ones I did. EG, remove capsicum, oregano and pineapple and then add on seasoned chicken and, say, prawns. Essentially getting 8 (with two that are normally surcharge) toppings for the price of a supreme, avoiding any extra topping surcharges. Even if you don't want that many meats, you could remove some meats and make it a vegesaurus. I was sad the day came when they stopped allowing you to add on a topping for each topping you removed (the supreme has 9 toppings but you can only get a maximum of 8 toppings with this method).
I've been doing this for a while now, experimenting with the limits of the online ordering system, and was wondering if anyone else caught on. If not, then I hope this helps :)
Its always been possible to change any two existing toppings into anything else without incurring surcharge with online orders.