Can I 'toe in' these cantilever brake pads?
You could try replacing your current pads with a set that come with double conical washers. It sounds, and looks, like this set of pads doesn't have them, but there appears to be enough space for you to install them.

The washers come in pairs, one concave and one convex, with enough "slop" to allow them to sit at an angle as the pad mounting screw passes through. Each pad would have two pair of the washers, one pair on either side of the brake arm.