OK Good news is that i just confirmed that what I suggested above about rewriting the user agent to trick the pinterest site into thinking it is on a desktop and not a mobile device does in fact work. Bad news is that both the caveats I was worried about along with a different one is also true.
1. You don't get sent to the app store as was the case before. - Good
2. The Pinterest pages don't render as well, at least on an iPhone. I suspect this is not as big an issue on an iPad. Bad for iPhone OK for iPad
3. You have to use a hybrid wrapper app that intentionally overwrites the user agent and masquerades as anything other than a mobile device. - I could tell you how to do that but then your brain might explode.
4. In my case anyway, Pinterest is still forcing me to login before viewing even someone else's open boards. And it doesn't do this on my desktop browser so there might be a way around this unless they have some other way of knowing I am on a mobile device
The solution could be to disguise the wrapper webview as being on an obscure mobile device with a browser that Pinterest does not have an app for. Like maybe Blackberry or Windows Mobile devices????