In a small, deep saucepan, bring the port to a boil over high heat; let it boil rapidly for a few minutes to burn off the alcohol. Lower the heat, add the sugar and water, and simmer, stirring until the sugar dissolves. Remove the pan from the heat.
Peel the pears and core them from the bottom, leaving the stem intact. As you do this, add them to the syrup. (The syrup should cover the fruit. If not, add more sugar syrup made from equal amounts of water and sugar.) Add the cinnamon, clove, cardamom, orange and lemon zest, and peppercorns. To keep the pears moist as they cook, cover them with parchment or cheesecloth.
Return the pan to the stove and bring to a gentle simmer. Poach the pears until tender when pierced with a skewer or knife, 15 to 30 minutes. Remove from the heat and let cool in the syrup.
Just before serving, beat the mascarpone, sugar, and Frangelico with an electric mixer until soft peaks form. Divide among four dessert plates. Arrange the pears on the mascarpone. Taste the poaching liquid and reduce to concentrate the wine flavor if necessary. Drizzle a little of the liquid over the pears and top with the hazelnuts.
You can cook the pears up to a day ahead. Cover and refrigerate them in their syrup; turn them once for even coloring.