SslStream equivalent of TcpClient.Available?

Based on the advice of @Len-Holgate in this question, I'm asynchronously requesting 0-byte reads, and in the callback, accept bytes the available bytes with synchronous reads, since I know the data is available and won't block. This seems so efficient and wonderful.

But then I add the option for SslStream, and the approach falls apart. The zero-byte read is fine, but the SslStream decrypts the bytes, leaving a zero byte-count in the TcpClient's buffer (appropriately so), and I cannot determine how many bytes are now in the SslStream available for reading.

Is there a simple trick around this?

Some code, just for context:

sslStream.BeginRead(this.zeroByteBuffer, 0, 0, DataAvailable, this);

And after the EndRead() ( which correctly returns 0 ), DataAvailable contains:

// by now this is 0, because sslStream has already consumed the bytes
available = myTcpClient.Available; 

if (0 < available) // Never occurs
{
    // this part can be distractingly complicated, but 
    // it's based on the available byte count
    sslStream.Read(...); 
}

And due to the protocol, I need to evaluate byte-by-byte and decode variable byte-width unicode and stuff. I don't want to have to read byte-by-byte asynchronously!