After a somewhat carefull analisys to my team, I was able to protect 15 riders, and didn't had that much trouble doing it.
I believe 15 riders should be enough for each team to protect, just prevent Blanczy from selection more than 1/6 (rounded down) from each team, meaning, I have 30 riders, so he would be able to select 5 riders from my team. If I had, for instance, 20 riders, he would be able to select 3.