Well I have to agree with the need for a little extra fuel.
If you put a "cell" in the under seat storage the weight should be low enough not to effect the balance of the bike. From there a hose with a shut off to the tank .
with the 400 it's a no brainier as the tank is down lower. I don't know about the the 650 but you could always use an elect. fuel pump if needed.
Personally I say do it. :!:
Beats the he** out of melting on the side of the road
:lol: