I would try a quick strike rig.
You can buy them or make your own, usually any bait or sporting goods store will be able to help you out.
Quick strike rigs come with two hooks, usually trebles.
I put the bottom hook through the cheek of the minnow, or between the nostrils. You want the hook point to be pointing toward the tail of the bait. the second hook usually goes through the back, just under the skin.
You want it to be in lightly so that if you give a quick jerk, the hook in the back pulls out, this puts most of your force into the hook in the front of the bait.
Northerns usually take a bait, make a short run, turn the bait to swallow it head first. This puts your treble hook in the right position to hook 'em. I wait until the fish starts to move away the second time, or set the hook if they are moving off at a good clip.
Hope this helps,
Wiener