When I was looking at lowering my FZ6, it was a (fairly) simple bit of maths to calculate this.
Working out the sides of the triangle formed betwen a) the wheelbase line and the side stand and b) the base of the side stand a point on the seat directly above the side stand.
This will let you calculate the lean angle.
Then work out how much shorter the bike will be and you should be able to figure out how much shorter the side stand will need to be to compensate.
Alternatively, there are side stands which have an adjustable length, although I don't know how strong they are.