[gitoby]

If the app is open source (or at least the source code is accessible), the user would proceed to the source repo, clone it, open the Xcode project and relink to the framework version of their choice.

Others have pointed out how it could work with closed source apps. It's a bit more complicated, but it certainly is possible.

[jacobush]

It would be prudent to advertise this expectation of the app developer hoping to use the LGPL version. (Whereas with for instance the MPL and other licenses, no such need exists.)