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:
To add to the other answers, if you want to go even more polite (i.e. a more formal setting or dealing with strangers) you can use 失礼します. It's more indirect too, rather than explicitly saying "get out of the way or move".
You may simply say
This however, is too polite: