Why should their deliberations be "secret"? ...
... Unless some dirty deals are being done.
Presuming there is a *valid* reason for secrecy, keep it off the god-damn Internet ... duh!
Give them dedicated circuits to the G20 server, hardware-based encryption/decryption, and VT-100s with appropriate keyboards and character ROMs. CKJV-type countries get a Linux dedicated appliances with appropriate fonts and keyboards.
If a diagram can't be expressed as character-based art, it doesn't need to be in the document.