Rengers answer is the correct one to accomplish what you want. However, the real correct answer is "Don't do that in the first place."
From a design perspective, a "Welcome Panel" or any kind of startup/splash-screen is a bad idea and the Apple Documentation tells you explicitly not to use them. Even for games, they're a bad idea that should be avoided if possible.
It's not a "Welcome Panel" it's a "wade-through-all-our-marketing-crap-before-you-can-actually-use-our-app" panel.
Mobile apps aren't like apps for regular platforms. Non-mobile hardware is faster so the obtrusive startup screens load faster and can be dismissed faster. Non-mobile apps tend to accomplish many task and people use them sitting down for prolonged periods. Users will tolerate a few seconds wasted clicking through startup screens so they can get into an app they will use for many minutes or even hours.
By contrast, mobile apps are often used by people on the go and in a hurry. The apps are small and ideally perform a single task. As quickly as possible, people need to be able to get into the app, perform what ever task the app accomplishes and then get back out again. If you're only using an app each time for 30 seconds or so, having to spend 5 seconds each time wading through startup screens is massively annoying.
Mobil hardware is slower and operations can take longer. Depending on its complexity and resources an app can take as much as 10 seconds to launch. In your case you want to add to a startup screen that has to load, connect to a url, display and then have the user perform an operation. That will take another 5-10 seconds minimum. So you're looking at users having to spend 20 seconds or more just getting into your app.
That doesn't sound like much but try mocking up your app and then using it on the go i.e. while walking, waiting for an elevator, going up the stairs, waiting for a red light etc. Test it in social situations. In the middle of conversation say, "Let me check on that" then take out the iPhone launch your app and try to get some information from it. 20 seconds becomes a very long time in all these circumstances.
Even shorter launch times are very annoying if you have to take some action every single time you open the app just to get to the functional part of the app. It's arguably even worse to spring a startup screen on them intermittently so they never know when they open your app how long it will take to get in it. User surprise is not good design.
Instead of forcing users to do something, you should embed advertisements and update notices unobtrusively in the app itself so that people can see them while they are using the app. In the case of advertising, this has the added advantage of putting the adds in view the entire time the user is looking at the app.
I don't know how many times some idiot from marketing has come in and started a feature request with, "We need to force the user to..." The only response to those types of request is to set the marketing weeny on fire. Do that several times and they'll stop trying to systematically alienate your customers.