ftp ftp.host1.com
login
ftp> proxy open ftp.host2.com
login host2
ftp> proxy put public_html/myfile.html public_html/blah.html (will copy myfile.html on host1 to host2 as blah.html)
ftp> exit
Correction:
ftp ftp.host1.com
login
ftp>proxy open ftp.host2.com
login host2
ftp> proxy get public_html/myfile.html public_html/blah.html
(Don't know how that ended up as 'put', sorry for the mistake)
ftp> exit