Export RSS Feed - Posts sequence

[Clodo]

Imagine this:
- Create a topic "A"
- Create a post "A1" under "A".
- Create a topic "B"
- Create a post "B1" under "B".
- Create a post "A2" under "A".

I need a RSS Feed that show 5 items, the posts/topic in cronological order: A2,B1,B,A1,A.

I have IP.Board 3.1.1, but i can't find information or settings about that.
It's possibile "out-of-the-box"?
I'm a developer, any suggestion (patch-style) will be appreciated.
Thanks!