We are a corporation. Therefore there is some statutory limitation to how an election is held.
What has been suggested can not be done how you proposed it.

You either have a postal vote, or a live ballot, not a combination of both.

If you choose to have a live ballot, then all those entitled to vote that cannot attend have to get someone to vote by proxy for them.
In most corporations, the non-attendee votes would be proxyed by the Company Secretary.
The problem is that the ballot is therefore no longer secret.

So aside from the logistics and legalities, the chances are that any additional voters gained by your method would be lost by those non-attendees who cant be bothered to fill out proxy paperwork and send it in.
While it may work in other organisations, just as we feel the majority of voters are people that frequent the bb's, I also think that the majority of voters already come to the convention, and already know most of the people that stand or are likely to stand for election.

I suggest you have a talk with Mr Rosenblum at the convention about the practicalities before you do anything further.
Not saying it is not a reasonable idea, just that I dont think it works.