It looks like sshfs is possible in principle, as my experiments' early results show. However certain parts are missing in Android. You need a port of libfuse, glib, and sshfs itself. Besides, dropbear's implementation of ssh does not understand the -s option (invoke subsystem), so path to the sftp-server should be given to sshfs as one of its parameters (and you need to know it beforehand, from your host's sshd config). I was able to put these things together (see
https://gitorious.org/android-pc) and got to the point when I mounted my home directory under /sdcard (SD card is absent physically), and could browse it via Android's file browser, even df command worked.
But these are, again, very early experimental results that I'd like to share here.
Thanks.