Just rename 'Fill' to 'Support'

Not enough players want to play support. This is an issue with the community of players more than the system. So here's what you do about it: 1: Stop choosing "fill" if you don't want support. 2: Choose "fill" and accept you will have to support often.

If enough people go with option #1, Riot will see this, and realize there is a problem when they see the number of people choosing it plummet. So what happens next? Riot has some options, but the best short-term fix would be the addition of "fill except X" option. Ideally, the long-term solution is to get more people into the support role. It's generally undervalued and underrespected by players. A good video/series by that would show up in the client about the importance of the role and provide guidance, should drive more players into the role, and make "fill" less likely to be pushed into support all the time.