My grandma always says, "そこ" when she wants someone to move, -usually she just says that to my mom or me- but I have heard that that translates more as a brusque, move than an, "excuse me". Would I just add ”ください” to the end to make it more polite?
そこ literally means "there" so you can't just add ください to it. For "move", I think you would say:
どいてください。(polite form of どいて, but still sounds informal)
(ちょっと、)そこ、あけて。 (Lit. Make room there.)
To sound polite I think you could say: