you're going to need some birth control, somehow. taking chances like that would be not only risky to yourselves, but also to your partners. if you didnt tell them she had no birth control, then it would be rather deceptive.
there are plenty of other birth control options, eg, diaphram, sponge, etc, which are relatively effective. of course, none are going to prevent the spread of disease, so you'd need to choose your partners carefully. here is a pretty comprehensive list :
http://www.plannedparenthood.org/pp2.../birthcontrol/
sometimes, a fantasy is best left a fantasy. if you're making it a reality, make sure you check the consequences REALLY CAREFULLY before you leap over the edge. if she got pregnant, would you both(!) be comfortable with an abortion, or alternatively, fathering a child who is not your own?