[kiritanpo]

Static linking of LGPL content (thus making it derivative work) only requires that it must allow "modification of the work for the customer's own use and reverse engineering for debugging such modifications".

Making your own code public is not the only way to achieve this.

You can also make available to customer object files and build instructions to recreate your software with the (modified) statically linked LGPL content. (if it's LGPL > 2.1 you have extra requirements: you need to provide all toolchains/dependencies and it must be actually possible to install a modified version on the hardware)

Granted, this is not commonly used but I've used this on some projects where dynamic linking was not available/desired by client.