First, you need to educate your competitors to get them working with you. When you show them how integration marketing is really about providing maximum value to the customer, you won't have competitors anymore. You'll have partners.
Second, you must be able to provide accurate metrics to show the profit potential of the relationship. In other words, know your conversion rate. Being able to tell your potential partner that your back end offer converts at a rate of 5, 10 or 15 percent is much more likely to convince him to do business with you than if you approach him with generalities such as "lots of people will probably respond to this offer."
Don't, however, inflate your numbers to convince someone to work with you. If you tell him that 10 people out of every 100 respond to your offer, he's going to expect that 10% conversion rate. Then if only 5% convert, he's not going to trust you, and your JV relationship will be finished. On the other hand, if you promise a 5% rate and it turns out to be 10%, he's going to be thrilled. So the rule is this: underpromise and overdeliver.
If you don't know what your metrics are because you've never offered a back end product before or because you've never integrated your marketing with anyone else, be honest. Tell him you can't guarantee specific numbers until you test. If you've educated him properly in step one, he should be able to see the potential for profit, so propose running an integration marketing test together. Then you'll have accurate metrics to show future partners.
Third, provide higher affiliate commissions than normal. Most affiliate programs only pay high commissions on the front end. Commissions on back end products are typically much smaller or nonexistent. But if you offer a 50% payout on a $1,000 product, that alone could be incentive enough for your competition to do business with you.
Fourth, make it extremely easy. If the process is complicated or they have to expend a lot of time and energy to get things set up properly, they won't want to integrate with you. Sign them up for your program. Write all the copy. Provide all the links. They shouldn't have to do anything more than "copy and paste" your messages into their system.
Finally, thank your partners often. Keep your name in front of them so they are constantly reminded how profitable it is to do business with you.