You can work out the front and rear roll centres using the calculator  save these values... Then apply a bit of trigonometry and consider the line of the roll center inclination to be the hypotenuse.
a = Subtract the rear roll centre height from the front roll center height
b = the wheelbase
A = tan1 of b / a
roll center inclination = A
http://www.mathsisfun.com/algebra/trigfindinganglerighttriangle.html
This would be a useful and addition to the calculator in the future... I'll add it to the list of enhancements.
