They could just create a list of players with permission to take the avatar. I think the way it's coded, it's not that simple - such a list would have to be a subset of avatar wardens or admin ranks, which of course defeats the purpose. I could be wrong though, feel free to pass it on and ask them :P.
How would it defeat the purpose when you would have a list of people that could be changed at a whim and don't necessarily need a rank to pull the avatar. Instead the players could be marked as a 'trusted' clan member with access to the avatar. This way the members don't have to worry about a rogue player hogging the avatar for purely personal gains. It could have its issues though especially with coding. Up until recently jagex hasn't exactly been using friendly coding allowing for implementation of newest aspects to older content which has posed an issue for smart development time consumption.