You could always come to Otogakure and become a synthetic sage. It has some trade-offs, but it allows you to insta-sage and stay in sage mode for a while.
But, talking about the topic, it's a hard thing to do properly. People aren't going to want to just stand still because everyone here moves faster than bullets. That means people are going to make ways to go around the problem of standing still by making 'batteries' where they just store their sage-mode chakra or it just constantly gathers sage mode because "it's not moving, I am".
So like I usually say, it's in the hand of the writer. If fairness is questioned, a third party can always be brought in to take a non-objective look at it. If rules need to be in place, Sabumaru seemed to have a pretty good idea with the '1 turn charge=2 turn active' idea. But then again, just because you're 'actively' in sage mode, doesn't mean you should be able to just throw a fireball the size of the moon. Once again, though, it falls back onto the hands of the writer to leer away from power abuse.