jrickards, I'm using dual pivot brakes without a lever made for them and there is only a slightly increased amount of hand force needed, you may or may not experiance the same result. They're still much better in braking performance than a single pivot.

AFIK only Tektro makes DP calipers with external nuts, R539 and R556 models (differences are in the reach). You might want to perform a search to verify this. You can also drill out the rear of the fork and the front of the rear brake bridge to accept an internal nutting mount.

Brad