multiple imapc settings in different namespaces

[abi at oleane.net]

hello all

i assume this question must have already been asked, but i'm looking for 
a way to circumvent which might work specifically on my system.

the version can be any available version between 2.2.9 and 2.2.22
(i'm testing with both of the above and no other )

i'm using imapc in 2 different namespaces.
in both cases, the imapc_host is local, and a custom passdb program is 
expected to handle proxying to different servers.
one of the case should proxy to a different legacy platform, and the 
other is used for shared mailboxes.

is there any way at all to be able to tell which is which in passdb ?
i don't care about the password, i can use a login prefix or suffix, 
different ports, different master passwords, ssl, maybe a different 
protocol name or auth method... somehow

i've seen in the source code there is a namespace "owner" but did not 
manage to change this parameter. i guess it is used internally.

anything else ?

thanks a lot for any help you can provide

best regards

@abi