I'm *still* arguing the letter of the law. "The charge" is "the charge." You are taking the spirit of a sidebar comment in the BRB over the very specific rules in the index.
To take another perspective, here: if you have to re-roll 1s to hit (as per a lot of little rules) and are shooting a plasma gun on overcharge but you *want* your guy to die, can you decline to re-roll the 1 you get? Say you get two 1s--can I re-roll one of them but not the other and achieve my aim?
The "some or all" thing you're hanging your argument on would allow you to *not* re-roll the dice at all if you didn't want to, which of course is against both the spirit *and* the letter of the rules.
I would argue that the same principle applies to Ere We Go: the charge is 2d6". If it is failed, you re-roll "the charge." Not part of the charge--the charge. It is notable that the word "can" is applied to Ere We Go--meaning you may or you may not, depending on other factors that may change your mind (overwatch, for instance). This would furthermore imply that, for other rules that lack such a modifier, the re-rolling is not optional. This, of course, contradicts the "some or all" principle as well--you don't have a choice.
I stand by my reading of the rules. The sidebar piece is a general overview accounting for variations in how re-roll rules are applied and when, not a stipulation allowing you to selectively interpret re-rolls to your best advantage.
Edit: Just to add some additional evidence to my interpretation here, the Runes of the Farseer rules (in the Eldrad or Farseer datasheet) take care to specify "any number" of the dice being re-rolled in a psychic test. If the default state of re-rolls were to follow the "some or all" thing, then no such stipulation would be required.