This winter I'll bring the S4 to the mechanics to do a work like this.
He is able to do the same on other bikes (check the
www.rmracing.it, he is my mechanic), it depends on the costs.
He can put the S3 short tail as the new R6 short tail.
The problem could be do the same of the picture, because you should mould the plastic parts or find a good fiberglass maker.
Let pass the winter and you will see.
with the new can the tail looks shorter isn't it?