I launched a membership site back in 2006 using a JV Giveaway. I believe I had around 700 jv giveaway partners participate in donating products they usually sold in return for the person who downloaded their product opting into their list.

Since I was the owner of the giveaway I was able to show a One Time Offer for my membership site to every visitor the 700 jv partners sent to the giveaway.

I ended up with over 3,000 members joining my membership site in only one week. So I used something similar and it worked very well for me.

I hope this has been helpful,
Steve Yakim