Beldum would breed the same as any other pokémon (other than the time to get it to hatch), so there is no way to get a shiny faster.
A good idea would be to go to the daycare at the battle resort, get 5 eggs, then cycle around the resort in a circle. This is easier because you can just dodge some obstacles, and keep cycling without any sharp turns. In fact, there is a certain spot where you can just keep holding up the controller and you'll automatically go in a circle. Basically, get 5 Pokemon, cycle until you hatch them, drop them off in the PC and grab a new egg (there should be a new one ready by the time you finish cycling).
Having a pokémon with Flame Body or Magma Armour will make all eggs hatch twice as fast, so that would be a great idea since you said you arent hatching a lot of eggs. I suggest Slugma, since it is easy to obtain, and both its abilities other than the hidden one are able to help hatch eggs. You can find it on the Fiery Path in ORAS with a 50% chance of encounter. You should have Slugma and five eggs in your party when shiny hunting.
Masuda's Method is a must-have for any shiny-breeders. Take a foreign ditto and breed it with your beldum to get better shiny chances. Here you can find out more, since I don't want to take too much space going into detail. Lots of websites have excellent explainations and a simple google can help you.
Use the Hatching O-Power. By using it more often, it also levels up, so the O-power will be pretty helpful for when your eggs take forever to hatch.
Use the shiny charm or oval charm. These can be obtained by talking to professor Birch after completing the National and Hoenn pokédexes. Shiny charm stacks with masudas method.
These are some helpful tips that make shiny breeding less of a headache. This guide is also great, but it is for XY so you might not be able to do some of the things it listed.
Edit: Forgot sources x3. They are:
-The links already provided
-Flame Body Info
-Magma Armour Info
-How Hatching O-Power Works
-My own experience :3
Good luck getting a shiny!