Thinning Sally Hansen's Hard-as-nails

[rodgerole]

I use both the black and clear Sally's fingernail polish for various effects on my fly heads and such, but I guess I don't use it quickly enough to keep it "fresh". My polish gets thick and won't penetrate as well after using it for a while, so I've tried thinning it with polish remover. Brands pf polish remover other than Sally's don't work at all and even the Sally's nail polish remover used as a thinner frequently causes milkiness that prevents the polish from going on well.
Does anyone know how to thin Sally Hansens' hard-as-nails without making it useless?

rodgerole

p.s. I know getting a new supply is the answer, but us old toots on fixed incomes are penny-pinchers.