TigerVNC is the only vnc client that seems to support proxmox's SSL encryption scheme.
If you're willing to install it on your client, run the following:
ssh -L 1234:localhost:1234 mimosa.tree.ewdev.ca -l root -- socat tcp-l:1234,range=127.0.0.1/32 exec:"'"qm vncproxy 119"'"
tigervnc localhost:1234