Place the chocolate chips in a large metal bowl set over a pot of boiling water (a double-boiler). Allow the chocolate to melt, with minimal stirring, 5 to 7 minutes. Take each cannoli shell and dip each end of the shell in the chocolate. Allow the excess chocolate to drip off and lay the shells out on a sheet tray lined with parchment paper or a wire rack so they don't stick.
Beat the butter in the bowl of an electric mixer fitted with a whisk attachment until it is light and pale yellow in color. Add the cream cheese and beat until well combined. Add the pumpkin puree, confectioners' sugar, spices and lemon juice. Mix until well combined. Place the filling in a piping bag fitted with a medium-size tip. Chill to allow the cheesecake filling to firm up, 15 to 20 minutes. When the mixture is firm, pipe the filling into the chocolate-dipped cannoli shells.