Hey John,
Sorry for the delay. Glad to hear you got things going from the other thread with the redirects and modal window going. Unfortunately, I don't know if there is any way to do a popup for the LinkedIn button with the way we do it. The Javascript plugin method that you mentioned *does* use a popup, but that's not how we do our Login with LinkedIn button. The main reason why is because the Javascript method *requires* an SSL certificate is installed on the user's site. That's not something we wanted to require of our extension, so that's not how we implemented things.
The Javascript method also works in a very different fashion than what we already have implemented, and so therefore isn't something you can simply add the <IN/Login> tag (or whatever it is) and get it to work with JLinked. It's annoying, and we'd love to have that flexibility, but it's just not there.
As for the iFrame with our PHP method, you may be able to do that. Never tried it though, so it depends on how much you want to dig. Mainly, when the Login With LinkedIn button is clicked, we call the "linkedInAuthenticate" function from the /components/com_jlinked/controller.php file. That code is only about 5 lines long, and the last 2 are performing the redirect. You could try using the first 3 lines to get the URL to redirect to and then showing that URL in an iFrame. That should work, but I'm not sure how the redirect will work when the user completes the login.
If that's over your head, just let me know and I can help you understand the iFrame a bit better.. I think you probably can take it from here though (gauging from previous conversations).
Thanks, and good luck,
Alex