I know mayo is a go to for sap. I would go over to optics talk too and post the question there as they are the optics group. Also, you might post on a couple of birding forums, they take their glass very seriously. The question is what will remove the sap AND not do any harm to those expensive coatings on the glass.
A call to the manufacture of the glass is always a good idea. Especially if it is higher end and/or under warranty. It would be a sad thing to void a good warranty because you used something unapproved...