Can you clarify why your rubber band trick isn't working? The pad's convex/concave washers should provide enough angle adjustment to get toe-in even with pad's angled tip. Maybe just a bit of patience and experimentation is what you need. It just might take three or four small adjustments to get it quiet. You could try setting one pad up parallel and one side toed in.
One option is to simply file down the protruding end of the pad.
I use the same pads on the rear. If I remember correctly, I initially set them up with toe-in, but due do the angled tip, the amount of toe in required resulted in pretty mushy brakes, so I wound up setting them up parallel to the rim. I had some initial squeal, but they quieted down with just a bit of adjustment and time. The angled tip really does make a difference when riding in the rain. The wet braking is much more effective and I don't get that grinding sound of the silty water wearing away my rim walls.
I use Kool-Stop V-brake inserts in the stock Shimano holder for the front brakes. I think I prefer the inserts/holders versus the pads for overall feel, but I liked the way the rear pads are curved, perfectly matching the curve of the rim.