Remove the windscreen, tape off the lower portion (you can even tape it off on a 'V' shape to match the lower fairing) and then paint the lower portion (spray paint or plasti-dip will work). Once it has dried you can use some weather stripping foam which has a sticky side and stick it to the windscreen within the painted area. Make sure to get the stripping that is tall enough to properly fill the gap with a little extra pressure to hold anything that might slide down.
Reinstall the windscreen and you're good to go.
Here's an example of the painted portion:
