I'm at the other end of the spectrum (25" frame) but basically have the same problem. In my case, it's also compounded by the fact I cannot have the brake arms too spread out because they will interfere with panniers.
I see a few possible solutions, apart from the one above.
1. If your heels do not conflict with the brake, unhook the cable off the right arm, remove the brake pad and change the position of the spacers.
(any of those near the top) should give you a clue.
On each side of the brake arm, there are two sets of washers: a thin convex one near the arm and a thicker concave one (thick on the sides, thinner in the centre). However the concave washers don't have the same thickness on the pad side and on the bolt side.
Simply swap the washers to put the thicker concave washer on the brake pad side, and the pads will touch the rim while the brake arms will stay a bit more open.
Ideally you should do the same transformation on both sides as it will look better. You may have to readjust the Spring adjuster bolts afterwards (this page
2. You could attach the rack struts on the inside
of the braze-ons. Bear in mind that the bolts will be a pain in the rear end to put in place and you'll need to tour with separate Allen keys rather than a combo wrench or multi-tool.
3. Back in the old days, we used P-clamps. Blackburn and MEC include some in their rack installation kits and if Tubus doesn't supply them, your bike shop should have them aplenty. Install the P-clamps on the seatstays a bit higher than the braze-ons and you will be fine.
It won't look that bad, especially on a dark bike (see this
. Still not as nice looking as solution 1.