Bonuses in scenes without a Tracker

Have you ever had players decide they need to make an Overcome roll in a scene without a Scene Tracker, so all the heroes who aren't making the roll all decide to generate bonuses?

This hasn't (yet) happened to me, but I know my players and I know this will definitely come up.  Is there a limiting rule I don't recall or is this just a "no, you can't do that."

I can see *some* situations where it makes narrative sense, but I can also see players asking why they couldn't all just add bonuses as a sort of "Take 20"?

Tbh I'm with the players here.  If there's no rush, why shouldn't they all put their heads together and make sure something gets done right?

If you don't want this to happen, then make it a montage scene instead of a full scene, or else just rule that they don't need an overcome for the thing in question - after all, the rules say you shouldn't roll when there are no stakes.

If there's literally no rush, then they can all stack bonuses infinitely and get a 12+ on every single roll.  That would indeed be a no-stakes situation and there's no point in rolling.

There's no rule against this, so you'd have to manage it some other way.  Making boosts off-limits in the absence of a threat of some sort would be one way.

The rules say you can produce one bonus by preparing for the next scene. 

I'd think to interprete that "one" very literally, thus not allowing any stacking (because that would require multiple boost actions).

Knowing players, maybe you'll have to remind them not to break the game. 

Or throw in a pointless scripted challenge first thing in the next scene, so the bonus gets wasted.