Having the daily opportunity to be in close vicinity to large passenger aircraft, I've started looking at how the aircraft designers do their aerodynamics... one thing I noticed is the nose cone 'stall strips':
And the underside aerodynamic treatment, which moves the separation point further rearward:
Note the slight widening of the underbelly, then it transitions into a narrower area that widens (at the blue strip) then narrows rearward. I'd taper that 'narrower area' upward to force the air underneath the body to exit more cleanly into the wake.
Now imagine a motorcycle with the same sort of underbelly. Take the wings and rear stabilizers off, put the rear wheel where the blue band extends across the rear of the underbelly, protruding just enough that if you get a flat, the body won't scrape. The front wheel would go just forward of the "U" or "V" shape in the underbelly, with a shortened nose.
Unfortunately, I have absolutely zero artistic ability... so using a CAD program or similar to mock something up is completely out... I might be able to mock up something rough using modeling clay, at least with that I can see in real-time and in 3-D what the shape is and change it as desired... those graphics programs always end up giving me some misshapen grotesquery that in no way looks like what I want it to look like... and the more I try to fix it, the worse it gets.
<sigh> This abortion is about the limits of my artistic abilities:
