You could do something different actually.
After this draft, the Rams are going to run the ball. That means Mason has quite a bit of value for the first part of this season. You could offer him Mason and thus he could handcuff the Rams running game, which could be elite this year. He could then keep Mason as Gurley's future handcuff, which provides value in the future as well as just this year. Mason on your team doesn't do much good once Gurley gets in the lineup, unless Gurley gets hurt. On his team he has more value.