You can cook it by mixing the mashed fruit with a bit of water to make a thick puree and simmering it at about 160F for 10 minutes or so, though that tends to lose some of the flavor and aroma. If your LHBS sells wine making supplies as well, then you could try this from the BYO article I mentioned earlier:
One way to minimize the risk of contamination from fresh fruits is to take a page from the winemakers handbook and sterilize the fruit with sulfur dioxide. Winemakers do not sterilize their wort by boiling it. They sterilize their must by treating it with SO2 (often in the form of Campden tablets). To sterilize a mini-must, mush your fruit into a slurry in a sanitized bucket. Add enough water so that its basically a thick liquid. Add one crushed Campden tablet for every gallon of your mini-must and let sit, loosely covered, overnight. During this time the SO2 will kill any microorganism in the mini-must, then diffuse away. The SO2 also acts as an antioxidant, preventing browning of the fruit. The next day, add the now-sanitized mini-must to your fermenter.
When I made my cranberry-apple lager I just racked it on top of the fresh fruit because it's 8.4% ABV, but with a lower alcohol content this may be the best option for you.