Alo mate,
You can get the stacking lines for about £3 a set, best place to get them is from http://www.thepowerkiteshop.com
They will advise you on how to link it up etc, dont ring up flexifoil for advice (i rang up ages ago and a the person on the other side didnt have a clue on what she was talking about, proabably a trainee or something!!)
I wouldnt reccommend using anything else, just in case they snap or something and crash land on a dog and poke its eyes out...dont risk it!!!
IDDI