You'll need a proportioning valve. Get 2 brake lines and a double bolt for the Master Cylinder. Run one line down to your front wheel. Get a short second line and a second double bolt to loop over to your other front caliper.
The second line will actually be 2 lines with a flare end on one side to fit the proportioning valve. This line will run to the back caliper. Adjust you proportioning valve so the rear wheel does not get as much pressure as the front.
The lever pressure at the master cylinder will regulate your front brake like normal. The proportioning valve will tune out the pressure to the back to whatever you have it set to. NOTE: your rear brake will always have less pressure at any lever possition then the front. In other words, if you give it full pull at the lever, the valve will limit it to half it's power (assuming you have it set to 50%). If you tap the lever your back brake may not do anything.