The ISS could be disassembled post retro burn to provide smaller pieces for burn-up. If the hull space were filled with a stoichiometric mix of propellant from the deorbiting vessel post-burn, it would autodetonate on re-entry.
This presumes that a discrete vehicle should be docked and use its thrusters to deorbit the ISS. A more obvious approach for a controlled deorbit would be having the ISS use its own thrusters on the Zvezda module, which is one of the ways that its orbit has been maintained over the years. However since these use hypergolic fuel (as do all of the visitors that have provided boosts such as the Space Shuttle's OMS engines) there's no way to pre-mix the propellants.
That aside, it's not obvious that a detonation in the habitable spaces will be helpful in reducing ground-impacting material: the most hazardous parts are dense and strong, such as engine bells and pressure flasks, and these are known to survive rocket explosions. And auto-ignition of the propellant by re-entry heat feels unreliable, relying upon that collection of tubes to hold together in the mounting gale of re-entry until it becomes incandescent.
So probably it's the mundane approach: a modest thruster burn to send the ISS into the "spacecraft cemetry" between NZ and Chile, far from substantial habitations. But if your modest proposal was adopted I hope it's timed for just before ground-level dawn in winter east of a major city such as New York so that many people can see the expanding vapour and debris cloud catching the early sun.