Hello Johnathan. Normally when I do a buttcap, I will braze a threaded coupler onto the material to screw on the threaded tang, or I will braze a stub tang on such as a bolt. The threads will anchor the buttcap and epoxy will grip the thread.
However since you don't have a torch, I would suggest the peened tang, and make sure the end of the tang is dead soft and just like Gabe said " Go Slow". Another method is to have the tang come through the buttcap and thread the end, then use a finial nut to secure the assembly. Another possibility is to have a hole throught the buttcap where you would have a long threaded nut, known as a finial, screw on the tang. You have to make sure that you have tight fit of the finial through the cap. I would try the peening and see what you think of it.
Here is a shot of a cap that has a coupler brazed on and is screwed onto the tang.
Good luck and have fun.
Brion