The QE barrels have an end cap that unscrews. As it's threaded, you could add an additional LDC but it would make an already very long gun into something that would be unmanageable for many.
The problem is that the QE system (and the the whole rifle) is really spec'd for the 22 so the built in baffle system is too thin for a 25. It's actually very effective on the 22.
You could try adding the Hatsan regulator instead. It should reduce the noise a little without increasing the length.
If it was me, I would buy one of the Hatsan LW barrels without the QE system. They come threaded so you could add a more effective LDC from NC without increasing the length. They aren't sold in America but there are a number of UK vendors that will ship barrels here.