Pete – I don’t know about the ACT but perhaps your namesake “Peter C” will jump in on that one, but in NSW a General Meeting has to be convened at a physical location that allows Proprietors to personally attend if they choose to do so, and any Owner who instead chooses to grant their proxy, can at Item 2 on the prescribed Form instruct, or more correctly place a limitation upon the matters that their appointee may vote on, and how they want that vote to be cast.
Whilst any proxies that your Executive Committee can successfully “harvest” would certainly count in terms of determining a quorum for the Extraordinary General Meeting (EGM), in order for those proxies to be validly exercised and be included in the ≥75% calculation to determine the outcome of the vote on that Special Resolution (i.e. a “poll vote”), the appointee must vote in accordance with the proxy-giver’s instructions.
So in NSW, the solution is to in the first instance find out from your Secretary or Strata Manager the “place where the Meeting is to be held”, and to then lobby your fellow Owners to ensure that they either physically attend OR that they note at Item 2 on the prescribed Form a “limitation” setting out how it is that they want their vote to be cast on the Special Resolution (and indeed on any other about which they have a preference).