What Jay described is pretty close to how we do it as far as building a leading link on the bike. If you can find specs on what the stock trail is that helps. Then you can decide how far you may want to move the front axle forward to reduce the trail to what you want. Keep in mind that ride height changes will affect final trail figures. So when you do the measuring also measure ride height.
Here is a leading link we did on a V Strom. Note floating calipers. This is the
better way to go.