Any item should say all vouchers can be used. For example the headnbody morph kits. If another artists created it, not DAZ, it is likely you can use it for upto 50%. Resold sw, for example, you can't at all I don't think. There are some nice models in the 1.99 discount tho. (The articulate dragon skeleton looks nice, no voucher tho)

No need to think outside the box....
    Just make it invisible.