Could you loop a couple of soft ties around the rails for her to hold?
way back in time, when I bought my C14, I did a review of a pilots backrest (which was a horrible p.o.c.) and took a picture you might find useful....
it seams that the seat actually may have been planned to have a "passenger grab strap" in place, like the old bikes of the 70's era. There are notches in the bottom edge of the pan, and also holes in the pan sub structure, that I'm sure were for that purpose... probably when they did it though, it looked hokey to the design artists, and they ditched the idea....
take a look, and think about adding a strap for the passenger's usage...
so we can find humor....
heheheheh I tried to hold back and not post this, but the more I think about it the funnier it gets....
get her on the bike, and slap a pair of these on each side....
then, you can go as fast as you want, and anywhere you want, and Never get a "kidney punch" from SHMBO....
so we can find humor....
Most likely used on the zx-14 as their seats have a strap. Get one of these and transfer what would be needed.
http://www.ebay.com/itm/ZX14-Seat-Front-Rider-seat-cushion-rear-seat-06-07-08-09-Kawasaki-ZX14R-/271249030102?pt=Motorcycles_Parts_Accessories&hash=item3f27b3bbd6&vxp=mtr
Or get one of those buddy belts.Buddy belt is out of bidness...... I have one I picked up in the UK but it looks like this may do http://www.2wheelride.com/llove_handle.html My GF loves this set up the times she is not on her bike. .
http://www.buddybelt.com/