I did some preliminary research on this topic and it seems there's some
opposition to implementing this feature (at least ten years ago there was).
This opposition is reasonable -- citing the fact that lwIP is meant for
embedded systems and this change would introduce code not useful to
everyone. But as I will likely develop my own procedure for this I'd like to
just toss this message onto the historical pile as one more person that
would like this officially supported.
The reason why it is useful for my case in particular is because I am
currently pairing lwIP with a network hypervisor (acts much like a VPN).
This pairing is intended to be linked into applications which may be started
or stopped in rapid and unpredictable ways.