polr (MASS): score test for proportional odds model

For the following model,

library(vcd)
arth.polr <- polr(Improved ~ Sex + Treatment + Age, data=Arthritis)
summary(arth.polr)

where Improved is an ordered, 3-level response I'm looking for a 
*simple* way to test
the validity of the proportional odds assumption, typically done via a 
score test
for equal slopes/effects over the predictors.

I do find a po.test= option in the repolr package for repeated measures, 
but for my
(tutorial) purposes this is too complex.  Did I miss something simpler?

Michael Friendly     Email: friendly AT yorku DOT ca 
Professor, Psychology Dept.
York University      Voice: 416 736-5115 x66249 Fax: 416 736-5814
4700 Keele Street    http://www.math.yorku.ca/SCS/friendly.html
Toronto, ONT  M3J 1P3 CANADA