I had a problem when I noticed my guitar only had one button for a strap, so I couldn't put one on. Luckily, I found a cheap way.
Step 1: Materials
The materials you will need are:
I) A guitar
2) A guitar hero strap
3) Some yarn (7 in. or more will be good)
Step 2: Attach It
You attach it to the bottom of the guitar as you would with any other normal strap (put it on the button). But on the top you attach yarn through the hole of your strap, behind the nut (don't put the yarn over the strings, duh), and tie it. Try not to get the knot at which you tied it under the strings.
Hint: You might want to tie the yarn around a couple of times, or tie some more yarn around.
Step 3: All Finished
Now you're done and ready to jam!