hmmm, I just use scp.
Okay, first of all why do you need mobile hotspot?

You know how to use sshfs - that's nice.
Just connect with n900 to your wifi network, as a client, get it's ip address by typing ifconfig wlan0 as root, and "mount" any directory from it via sshfs from your desktop.

However, as sshfs just emulates every action I would use nfs, and there is a thread which describes how:
http://talk.maemo.org/showthread.php?t=53164