Proprietary use possibility

[mr2160]

Hi,
as I understand the LGPLv3 licence the main thing you have to abide by is letting the user use a modified version of the library with the proprietary app. This library makes such use possible for the original libserialport library - it is imported as a dynamic library. But this (dart) library is also under LGPL, which would mean it is necessary to make this library modifiable too. Importing and building the application isn't an option then. How would one satisfy the licence requirements in dart? Or is it only possible by exposing the source code of the whole app?