As with any recommendations, I try a small section on a test piece first. But whatever you use, I would follow up immediately after by cleaning the glass with an isinglass marine cleaner/conditioner.
I've heard of Pinesol used on boat isinglass (never tried it myself): soak a Q-tip with pinesol and rubbed it on the sap for a few minutes. Again, I'd wipe with water quickly after, and then treat the window with a cleaner/conditioner.
One of the Boat Yards down the street uses the hand cleaner auto repair shops use to clean their hands - they use it for any grease or oily smears on isinglass windows. Think its 'gojo'.
EDIT: Link added (and its the one without the pumice/grit)