Simple, have the Safavids, or Sassanids implement a policy of installing 5-year governors of new territories, or territories taken from rebellious nobles.
Employ loyalist governors, and begin to ensure they use Imperial Troops rather than locals.
Frankly I don't know who would have the easier job of it. The Sassanids don't have gunpowder, but have a better rep, and technology that is high-end for the period, whilst the Safavids had gunpowder, but at the lower end for their period.
So, Sassanids centralize, try and foster a nation state, governors, Imperial Army. Small bits at first, eventually taking the entire state.