One of the most frequent complaints from subscription sites selling iPad and iPhone apps is that Apple refuses to hand over any customer information — not an email address, not a credit card number, nothing.However, some publishers have found a way around this marketing dilemma.Publishers that promote and sell “digital” subscriptions through their website, like Strategy + Business, are able to capture customer data when subscribers pay through their site. Apple (and Google) will then allow paying subscribers to download the publication’s app. Furthermore, Apple and Google will not take their usual 30% cut, leaving more money in your pocket.Many app developers strongly recommend making your app available through Apple Newsstand and Google Play because it gives you app some credibility (and prospects are less likely to be concerned about malware and viruses if Apple and Google give you a stamp of approval by listing your app). But given the reluctance from Apple and Google to hand over customer data that would improve retention and facilitate upsells, publishers shouldn’t just rely on the app stores for sales, and should be promoting their own digital products.However, there are ways to get customer information from Apple Newsstand buyers even if Apple won’t give it to you — namely by prompting customers to offer it up. Find out how Strategy + Business created its own work-around in this week’s Case Study on Subscription Site Insider.