I can make the cake fine and cover it in icing and even make the nipples as requested but what to use for the bra? I have no piping skils so only use fondant.
They want the cake as 'tacky' as possible.

I love these 2 (hope the links work) but think they are piped.

http://cakecentral.com/modules.php?name=gallery&file=displayimage&pid=1198687
http://cakecentral.com/modules.php?name=gallery&file=displayimage&pid=1221358


Any ideas?

How about using fondant and making a peep bra where the nipple is showing over the top rather than a lace type effect.

http://www.janssweettemptations.co.uk/images/boob%20cake.jpg

http://4.bp.blogspot.com/_f_K9ZIgmjYo/STcMDNmOJ6I/AAAAAAAAADA/2taUL0Plm9c/s320/DSC04257a.jpg

Those are piped, but it really doesn't take much skill to pipe squiggles like that on a boob cake. Since you prefer using fondant, I would cut strips of fondant to be the outline of the bra, then pipe the squiggles in between the outline.

Here's another option that was really easy to do http://farm4.static.flickr.com/3373/3552028576_7176ebc870_o.jpg

Great suggestions, thank you

CHECK OUT U TUBE THEY HAVE A LOT OF STEP BY STEP VIDEOS ON BASIC PIPING, FLOWERS, FONDANT, AND GUM PASTE. THEY HAVE BEEN VERY USEFUL TO ME IT MAY WORK FOR YOU TRY IT. GOOD LUCK!