I don't think jsciv was saying you couldn't. I think what the OP was asking was "If I have an ally in my hand that says 'Recharge this card to add 1d4 to your stealth check', but I'm not making a Stealth check, can I just recharge it anyway? I have too many cards in my hand and recharging it would let me get a card out of my hand without having to discard it when I reset my hand."
The question was whether he needed the "check" at the moment, not whether the die/bonus the ally gave was necessary to win. You can totally "overwhelm" the check. But you can't play an ally that effects a check if you aren't making that kind of check.
Rulebook v3 p9 wrote:
You may not activate a power that doesn’t apply to your current situation. For example, you may not play a card to reduce damage when damage is not being dealt, or play a card to evade a monster when you are not encountering a monster.
So you may not play a card to add to a Stealth check if you are not making a Stealth check.