Since VARs can be estimated as independent equations, omit -auto could be
used. Or you could apply a OLS stepwise selection method to each equation,
or use AIC or BIC to select the best specification from a set of
candidates. Maybe someone has a script to perform the steps, but I doubt
anyone has set this up to be as simple as --auto.for a system of equations.
One reason you may not find anything as simple as an --auto option for VARs
is that data mining of this type (setting zero restrictions) is counter to
the VAR modelling philosophy. Also it is rarely necessary because setting
lag coefficients to exactly zero when the OLS estimates are statistically
similar to zero will typically have few statistically discernible effects
in the performance of the entire system (that's why they are
statistically insignificant).
GRETL does have a VAR lag selection tool that does not violate the general
VAR model building concept, but this is probably different from what you
desire. Lasso in R might be the most reasonable alternative, especially if
you are using the VAR to forecast.
Or consider Bayesian VAR modeling that lets you shrink the lagged
coefficients toward around priors that are centered around zero. Check out
Nobel prize winner Chris Sims R code to implement (
http://www.princeton.edu/~sims/#VARtools)