In the Nether, your island is netherrack. The netherrack is chisel 2 which won't allow you to make the Hellfire Furnace unless you chisel it back to normal netherrack. You can't make a chisel 2 chisel unless you get iron/diamond/obsidian. Could you make it so you can use chisel 2 netherrack to make the Hellfire Furnace?

No. If you can't make it, that means you're not supposed to. When you are able to make it with netherrack, that is the appropriate time.