[R] Setting a pdf reader different from acroread under *nix

[Vittorio.De.Martino.vdemart1 at tin.it]

Under FreeBSD 6.2 I installed R 2.6.0.
Trying to load e.g. vignette("zoo")  R calls acroread automagically. 
I instead would like to use the lighter kde built-in pdf   reader kGhostView-
Is this possible?

Vittorio