A dilution of 1:3 (one part toner, 3 parts water or per AA, HCA) will increase the contrast most notably in the highlights. Refix the negs in plain hypo and then direct in the toner for between 3 - 5 minutes.

Run some tests first because the effects are of course irreversable.

I've toned both "regular" negs and PMK Pyro negs with good results.