I have a 27-year-old Yamaha FG-335II that I'd like to be able to use while standing up, but unfortunately it only has the single strap button on the end. I would rather not stick a new button on the heel of the neck simply because it is an aging guitar and I don't want to risk any modifications that might compromise the wood's durability.

I have tried attaching the strap to the neck, but I just don't feel comfortable with how the strap rests precariously on my shoulder. It feels too much like it's about to fall off the back, which is distracting to say the least. I've tried shortening the strap, which does help some, but by the time it's short enough to help I can hardly breathe. Does anyone else have this general experience as well? If so, have you found any ways to counter-act the problem?
What I did was, I took some kind of chord (In my case I was in a pinch and cut about a 6 inch string from one pair of my shorts :P) then tie it to the hole on the strap and tie it under the strings just above the nut.

I mean I don't go nuts with it when I use it, but it's always held up for me. Hope something works out for you.