I'm actually surprised it doesn't have a BIOS option for this - my ASUS Z77 board does. I have noticed, though, that it was much harder with my machine (before I extended the time to enter the BIOS from the defaults) to get in to the BIOS following a warm reboot versus a total shutdown and restart via the power button. Maybe it is a UEFI thing.
One thing you might try is to set the option in the BIOS to display the Gigabyte logo at startup (I'm sure there has to be an option in there to do that as every recent Gigabyte mobo I've seen recently seems to, anyway) to see if it increases the amount of time you have available to press the DEL key before the OS starts. The downside is, if it does extend the time available, you are routinely going to have longer boot times.
Another thing to try is to plug your keyboard in to other USB ports to see if you can figure out which one is being initialized first by the BIOS.