From the Like-Like room at the start you can clip out of bounds with the like like using the hookshot. By jump slashing as soon as you clip through the wall you can land in the unloaded darunia room. From here you can Super Slide and clip back into the like like room on the other side of the gates and head to the next room where the megaton hammer is.
Again from the like like room, use the like like to clip out of bounds into unloaded Darunia room. From here you make your way to where the boss door is and do a ledge clip to get under the platform in front of the boss door. Then you begin to bombchu or bomb hover up into the loading zone.
The hover for the Blind Fire Temple Boss Key skip can be a little dangerous due to when you use a bombchu just under the loading zone the bombchu will latch onto the solid ground of the loading zone and trail away. So you have to use bombs to get the last bit.
To know if your near the loading zone floor you can shield drop a bomb and it will land on the loading zone floor.