I would argue that the EEVblog audience is much broader than just the high-commenting members of this forum. As a low-commenting lurker who really enjoys your videos, the amp-hour podcast, tweets, and the electronics community in general, I hope you can find a way to include people like me in the giveaway.
Reserving one of the scopes for the patreon and forum supporters is a good gesture to your inner circle, but making the second one available to a more broad audience would be cool.
Maybe using the forum as the sign-up mechanism for the giveaway would be a good way to handle submissions and weed out bots etc.
As for how to handle the giveaway, one idea is to assign entrants particular ticket numbers, and if you meet certain criteria you will be assigned more ticket numbers. For example, normal entrants get 1 ticket, high-commenters get 3 tickets, patreon supporters get 5, etc. Then a script could pick one random ticket.