What I could see is Amaris manipulating a candidate of his own choosing into the position of SLDF Commander to replace Kerensky. I believe he did this with the bureaucracy of the Terra like the Hegemony High Council to setup his quisling regime. He would realize he doesn't have the votes on the Star League High Council and pour poison into young Richard's empty head about this much as MA suggests but there has to be a candidate who is favorable to him in the SLDF. This person would have to be a high officer in the Star League perhaps someone Amaris may have already helped earn rapid promotion or favored position. He or she is not likely personally loyal to him but may have done something in their past to jeopardize their career, social standing, family, wealth, etc to put Amaris in a position to control them. Now Kerensky did take great pains to streamline and organize the SLDF meaning undesirables (Social Generals) and the like would be rare but every organization has at least one. So yes I believe at least one or even a few dark horse candidates could exist in the SLDF of 2765.
So can this "dark horse" candidate be advanced? Again their rank would need to be sufficient and that might be tough for someone Amaris helped directly as Kerensky would notice and likely quash said career. So unless we are going to "enhance" his resume with some Battle of Gotterdamberg (the battle the RWR didn't really fight against a Periphery BattleMech Division) experience which might draw too much suspicion we need someone appearing genuine. So what our schemer Amaris needs is a high officer in the SLDF who can be "leveraged". Remember Kerensky kept his family hidden for a reason.
Now the High Council can be manipulated by Amaris for his own ends. I agree with Ice that the House Lords wouldn't mind a poor candidate that allows them great influence over a weaker SLDF it would advance their own agenda. Don't forget that Amaris frequently used the Lords distrust of Minoru Kurita as a point to advance. Kurita hated Amaris and perhaps he might be driven to hate this candidate convincing Lords like Steiner and Davion to back such appointment. So there is a lot to work with here...