A quarter-inch sounds a little tight.

Something made especially for mounting full fenders full-time in that situation are Reacharound Fender Brackets. I use them on the back of one of my bikes, but they come in a set for front and back.

You cut the fender and trim it to match the brake. Drill it for the brackets, then mount. They're actually more sturdy than the brake bridge fender bracket that came with my SKS Chromoplastics Longboards. And the fender works just great. I've had them on only for a couple of years, so it's too early to tell if there are long-term issues with the brake, although there shouldn't be.

Here's how it looks