This method works like a champ and is easy peasy. In fact, I just did this today on a folder back spring. With the spring in a vise as a heat sink, I could make the spot I wanted to drill red hot while holding the other end with my bare hand.Wrap the blade portion with a cold wet cloth and spot heat the tang with a propane torch in the hole locations, then drill. Won't take much or long. If you keep the blade cold you should not lose the hardness/temper.
Or purchase and use carbide drill bits.
That's exactly how I managed to get the holes drilled. ThanksBuy some carbide tipped masonry bits. You can get down to 1/8" I believe, and normally they're fairly affordable. Don't expect the precision of a standard twist drill bit (the hole will be a little bit larger), but it will get you through a hardened tang just fine.
Was a learning experience for me. Not too bad of a mishap given it was my first knife. I learn a bit more with every one.I did something similar on a batch of knives awhile back. I got them back and realized that the holes were all wrong. I had to walk out of the shop for a while. I did a few with masonry bits 1/4" but ended up buying several 1/8" carbides. Wasn't too big of deal