On the pineapple front, I have some not so great news, firstly it has to be fresh pineapple. I remember chating to mel and she said how she had been eating tins and tins of the stuff. Unfortunatly what you need is the enzyme in pineapple which is lost in the tinning or jucing process. Also, to get enough of it to actually have an effect means muching your way through about 7 of them!! So pineapple probably isnt the best way to go.
Sex is the best, as not only does sperm contain posgladulins (sp?) that can start of contractions but the penis ahm, 'massages' the cervix to help soften and dialate it, if you dont have a man at the mo, or you just dont fancy trying to engage in whale sex, try using a vibrator!
Also anything that sets the bowels off is a good bet (like a hot curry) as the uterus and bowels are closely linked they set each other off, hence why its common to suffer the squits in early labour. Do not however try to use caster oil to do this, as not only does it give you very nasty dioreah and dehydrates you (making labour even harder cause you cant keep fluids inside you) but it also causes foetal distress and crosses the placenta so baby can poop in its fluids and inhale it.