A client of mine who has recently given birth has been breastfeeding through pregnancies 2, 3 and 4 (this is baby #5).  The term used in Australia is *Tandem feeding*, although I don't know if that is used elsewhere.  This woman had weaned her 3 year old at about 6 months into the pregnancy, and continued to nurse her 18 month old.  Labour (this time) began spontaneously at 38 weeks
I spoke to her about how she will manage the two children at the breast.  The method she uses was recommended to her by a NMAA (Nursing Mothers' Association of Australia) Counsellor.  The new baby will have both breasts while mother is in hospital, then he will be kept to his breast, which happens to be the left.  The toddler has had the right breast as his since birth. 

In my midwifery practice I sometimes encourage women to use nipple stimulation to encourage the onset of labour.  I ask the woman to use gentle touch of her nipples, not expressing colostrum, and to work on stimulating a contraction about every 5 minutes for an hour.  If she is really ready for labour her body will take over, and contractions will occur spontaneously.  If not she can try again some time later.  The process is augmented by sexual foreplay.  
The big value of this system is that the woman controls it.  It is less effective if the presenting part is poorly applied, so being upright, walking, being active, are all part of success.
There is a very interesting section about breast stimulation to induce labour in Henci Goer's book Obstetric Myths vs Research Realities (1995).  The two papers for which abstracts are given are
        Elliot JP and Flaherty JF. The use of breast stimulation to prevent postdate pregnancy, Am J Obstet Gynaecol 1984; 149(6):628-632.
        Salmon YM et al.  Cervical ripening by breast stimulation.  Obstet Gynaecol 1986;67(1):21-24.

Joy Johnston, Midwife IBCLC
Melbourne Australia