There is no way to distinguish between the two. The "s" in "Elles" is silent unless followed by a vowel sound (which "c" is definitely not), and the "ent" ending is completely silent, so there's no difference between the two except for context. I'm reporting this, but it still isn't fixed on January 5, 2014, so I'm doubting that they'll fix it...
It is now 6 November 2014 and the singular is still marked 'wrong'. Will report.
It's unlikely that "squash" would work here, because of the material that glasses are made with: glass - something that would shatter if broken. You could use "smash", perhaps, or for that matter, "shatter". (But "quash" would not work at all. "Quash" means "to overrule")