Well you strip all the crap off, don't you? Just run the barest frame possible.

You still have the problem that the bits that you cannot just knock up out of old Morris Minor steering columns or AK47 barrels are the bits that break.

I know one person who has legitimately worn out a bike frame, in 40-something years of cycling, and it wasn't me. It was a guy who rode his bike about 50 miles *every single day* and rode from Edinburgh to Glasgow and back a couple of times a week. Eventually it started cracking around the welds.