So you want to use an obsolete version of a EDA
tool not meant for IC design, to do this? Why?
If you did a control-section variable loop and
plotted afterward, you ought to get what you
want.
On LinkedIn there's a guy "LTSpiceman" putting
up tutorials about using LTSpice for more complex
analyses, like Monte Carlo. This would be a way-
degenerate case of that (only one process param
afffected, and determinstically).
I'd bet that the LTSpice "formerly Yahoo!" group
would have stuff on this, buried in the mound of
chatter.
ltwiki.org might be a good place to start.