A virtual server which caters to both HTTPS and plain TCP traffic on the same port.

Try this code:

when CLIENT_ACCEPTED {
    SSL::disable
    TCP::collect
}
when CLIENT_DATA {
     Store TCP Payload up to 2^14 + 5 bytes (Handshake length is up to 2^14)
    set payload [TCP::payload 16389]
    set payloadlen [TCP::payload length]

    if { [binary scan $payload cH4Scx3H4x32c tls_record_content_type tls_version tls_recordlen tls_handshake_action tls_handshake_version tls_handshake_sessidlen] == 6 && \
        ($tls_record_content_type == 22) && \
        ([string match {030[1-3]} $tls_version]) && \
        ($tls_handshake_action == 1) && \
        ($payloadlen == $tls_recordlen+5)} {
        SSL::enable
    }
    TCP::release
}