Wishazu,

You don't have to wait for an Avatar to come available "in game" to play in the Upper House....only if you intend to take part in the active game in the lower house.

Once you have an Avatar, it is possible for you to go from Upper to Lower house and put yourself forward as Consul (active player) in elections.

I've chosen a Spy Avatar for my Upper house role as I know I will not be able to take an active part in this game....potentially ever. It's all pending Computer upgrading etc so I've chosen an Avatar that is "in game" but I don't control........

.......however, I can still influence the Avatars role "in game" via my Senate speeches.