isn't the whole idea of a HOF for national teams to be increase interest and curiosities from the community? if that's the case, I don't see any way other than handling the voting rights to all national managers. Make the news on the front page, and have everyone vote in, or else the change probably doesn't worth the effort to code it.
If we are worried about personal bias, just don't allow managers to vote for their own players or give every manager three votes instead of one, but we need to INCREASE participation, not restrict it