sounds like you want to use sshfs. To mount a directory or partition from hostb on hosta while currently logged onto hosta you could do:
mkdir -p /path/to/somewhere/hostbdir
sshfs user@hostb:/path/to/some/dir/on/hostb /path/to/somewhere/hostbdir
Now any program can copy files to hostb while on hosta just by dropping files into /path/to/somewhere/hostbdir/
To unmount it you can do
fusermount -u /path/to/somewhere/hostbdir
Caveats: this requires fuse and sshfs on hosta (only sshd on hostb). I do not know what packages provide these on slackware. Also note that at least in Debian the user using sshfs needs to be in the fuse group.