Although he will probably be forever known as the acquirer of the rumored $6-million Whoopi Goldberg book, Rob Weisbach is determined to show diversity on his Morrow imprint list. Case in point: he recently approached U.S. p t laureate Robert Pinsky to edit a collection of p try under the tentative title The Handbook of Heartbreak. Pinsky, whose own p try is published by FSG, will pore over three centuries of verse to select over 100 verses about this adversity. Weisbach negotiated the deal with Pinsky's new agent, Jill Kneerim of the Boston-based Palmer &Dodge.