mail.nntp.newsrc property

I tried setting the mail.nntp.newsrc property but I found this is did
not work and was not implemented.
There doesn't seem to be very much special code for the case that it is
not set.
If the mail.nntp.newsrc property is difficult is it possible to have a
mail.nntp.newsrc.dir property so that it is possible to move the
directory that .newsrc is stored in?
I'm trying to write an application that has multiple identities and I
want to have all the nntp subscription details separated.

Any work around would be appreciated.

Thanks,
Hash9