Sorry I forgot to explain the changed syntax.
Here is the help section:
--invoke-diff-cmd ARG :
use ARG as format string for external diff command
invocation.
Substitutions: %f1 %f2 files to compare
%l1 %l2 user defined labels
Examples: --invoke-diff-cmd="diff -y %f1 %f2
--invoke-diff-cmd="kdiff3 -auto -o /home/u/log \
%f1 %f2 --L1 %l1 --L2 "Custom Label" "
The switch symbol '%' can be modified by defining an
alternative symbol string, starting with '#','$' or '-'
Example:
--invoke-diff-cmd="--- diff -y ---f1 ---f2"
