I'm hearing ya, but if part of the issue is from a big pump being pulsed by a speed controller than you'd want to rectify any irregularities prior to feeding the rail I would have thought?
If the issue is in the rail only then it must be fitted to the rail.
Not sure on how these dampeners are designed, but would they possibly be able to absorb some of the rail pressure once on boost thus affecting the total amount of rail pressure to feed the injectors correctly ?