You are right in that check-in opens for 3 hours prior to departure for international flights departing MEL (and possibly an extra 30 mins if operated by an A380).
Is your husband also travelling with you? If so, if you do online check in and have him check the bag in as his own without you there whilst you proceed through to the lounge. That should work. If he isn't travelling, I very much doubt an agent would allow him to drop a bag for somebody else.
