reading nndoc without being connected

[John <falseaddress@nospam.nomore>]

Hello

I set up a nndoc in my Group buffer using the commands;
G f
M P b
B r

in-order to load a 42MB mail archive to be able to search and view
articles.
It works good, but it takes a long time to load, I have a 256 km of
ram. my question is, is this a correct way of doing it?

also, I tried to view the file without being connected to the web but
I don't know how even after reading some docs.

while I am connected or not;
M-x gnus-no-server (stills want to nntp: read 1150k).
if I issue the above command while I am not connected it will not show
any active groups including my nndoc.

C-u M-x gnus in-order to select the server still wants to nntp: read.

any idea how to read this some.mbox file with out being connected and
without having to nntp: read some 1150k, in-order to search and read
articles? 

thanks