Instead of waiting until your bladder is full just start peeing when you feel a little bit of an urge to urinate.
If you start just peeing whenever and not holding the urine in you should start wetting your pants or diaper without knowing about it or having to think about it.
It took me a few months but eventually I started to become diaper dependant and wet my diaper without having to force it.
Now I wet my diaper without even realizing it.