A: 

This is rather a PBS question; I usually make an R script (with Rscript path after #!) and make it gather a parameter (using commandArgs function) that controls which "part of the job" this current instance should make. Because I use multicore a lot I usually have to use only 3-4 nodes, so I just submit few jobs calling this R script with each of a possible control argument values.
On the other hand your use of pbsdsh should do its job... Then the value of PBS_TASKNUM can be used as a control parameter.

mbq