C-u 100 SPC (selecting groups)

[Daniel C. Bastos]

I can say C-u 100 SPC on the group buffer to tell Gnus to download the
last 100 articles, but I'd like to automate this; whenever I press, say,
RET on a group, it will know I want the last 100 articles.

I could write a function that passes the number I want and bind that to
the RET key, but I would think that there's a standard way of doing
this. Pointers?