use of pedigree structures

The lmer function includes random terms as

(expression for a model matrix|grouping factor)

and I wonder how general the expression can be. For example, a pedigree 
object can be converted to an A matrix (in the language of animal 
breeding), but can the A matrix be incorporated into an lmer analysis?

I thought that

(chol(pedigree)|ones)

might be OK, where 'ones' is a constant vector of value 1. With the only 
example I have tried, the syntax is accepted but the analysis ends with 
a forced exit from R (core dump).

I White
  University of Edinburgh
  Ashworth Laboratories, West Mains Road
  Edinburgh EH9 3JT  (Tel 0131 650 5490)