You can mount another ram disk at /home/ftp which is not read only (as is done for the /tmp and /var directories) which will allow you to have a small filespace to do transfers. You can look at the rc script in /etc/rc to see how this is done (first expand /ramfs.img to /dev/ram[2|3] then mount -n /dev/ram2 /home/ftp). You can also use the ext2 fs tools to manually format the ram drive (which is what the expand /ramfs.img is really doing if I'm not mistaken) which may allow you to eek out some more space by tuning the parameters to your typical use. I haven't personally needed to do this though.
Tuck